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Amendment No. 4

Ultra Clean Holdings, Inc.

150 Independence Drive

Incorporating Services Inc.

Copies to:

     Approximate date of commencement of proposed sale to the public: As soon as practicable after the effective date of this Registration Statement.

     If any of the securities being registered on this form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, check the following box.    o

     If this form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.    o 

     If this form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.    o 

     If this form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.    o 

     If delivery of the prospectus is expected to be made pursuant to Rule 434, check the following box.    o

CALCULATION OF REGISTRATION FEE

     The Registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment which specifically states that this Registration Statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until the Registration Statement shall become effective on such date as the Commission, acting pursuant to said Section 8(a), may determine.

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SUBJECT TO COMPLETION, DATED MARCH 24, 2004

6,000,000 Shares

Ultra Clean Holdings, Inc.

Common Stock

     Prior to the offering, there has been no public market for our common stock. The initial public offering price of our common stock is expected to be $7.50 per share. Our common stock has been approved for quotation on The Nasdaq National Market under the symbol “UCTT.”

     The underwriters have an option to purchase a maximum of 900,000 additional shares from the selling stockholder to cover over-allotments of shares.

     Investing in our common stock involves risks. See “Risk Factors” on page 7.

     Delivery of the shares of common stock will be made on or about                     , 2004.

     Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is                     , 2004.

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      You should rely only on the information contained in this document or to which we have referred you. We have not authorized anyone to provide you with information that is different. This document may only be used where it is legal to sell these securities. The information in this document may only be accurate as of the date of this document.

Dealer Prospectus Delivery Obligation

      Until                     , 2004 (25 days after the commencement of the offering), all dealers that effect transactions in these securities, whether or not participating in this offering, may be required to deliver a prospectus. This is in addition to the dealer’s obligation to deliver a prospectus when acting as an underwriter and with respect to unsold allotments or subscriptions.

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PROSPECTUS SUMMARY

      This summary highlights information contained elsewhere in this prospectus. This summary may not contain all of the information that may be important to you. You should read this entire prospectus, including the section entitled “Risk Factors” and our consolidated financial data and related notes, before making an investment decision. References in this prospectus to “Ultra Clean,” “we,” “us,” “our” and “our company” refer to Ultra Clean Holdings, Inc. and Ultra Clean Technology Systems and Service, Inc. unless otherwise specified. The Ultra Clean Technology logo is our registered trademark. In addition, this prospectus contains trademarks, service marks and trade names of companies and organizations other than Ultra Clean Holdings, Inc.

Ultra Clean Holdings, Inc.

      We are a developer and supplier of critical subsystems for the semiconductor capital equipment industry, focusing on gas delivery systems. We develop, design, prototype, engineer, manufacture and test gas delivery systems that enable the precise delivery of numerous specialty gases used in a majority of the key steps in the semiconductor manufacturing process. Our products control the flow, pressure, sequencing and mixing of specialty gases into and out of the process chambers of semiconductor manufacturing tools. Our customers are primarily original equipment manufacturers, or OEMs, of semiconductor capital equipment. These OEMs outsource the manufacturing of their gas delivery systems in order to improve the efficiency and reduce the costs of their design and manufacturing processes. Our system designs are reconfigurable and can accommodate different components and additional functionality with each new generation of semiconductor devices. We do not sell standard systems but design and develop each product in collaboration with our customers. We had sales of $84.3 million and $77.5 million for the years ended December 31, 2002 and 2003.

Our Solution

      We offer our customers:

      A complete outsourced solution for gas delivery systems. We provide our OEM customers with a complete outsourced solution for the development, design, prototyping, engineering, manufacturing and testing of advanced gas delivery systems. Our engineers work with our customers to customize and improve the design and performance of their gas delivery systems, in addition to ensuring that our products comply with applicable safety and environmental regulations and industry standards. We also manage supply chain logistics and perform comprehensive testing and qualification of final gas delivery systems to help our customers improve their manufacturing efficiencies, design-to-delivery cycle times, capital utilization and product operating characteristics.

      Improved design-to-delivery cycle times. Our strong relationships with our customers and familiarity with their products and requirements help us to reduce design-to-delivery cycle times. We have optimized our supply chain management, coordination of design and manufacturing stages of production, logistics expertise and manufacturing controls to reduce design-to-delivery cycle times, allowing us to rapidly respond to order requests and quickly reconfigure product designs to meet end-users’ constantly changing requirements.

      Component neutral design and manufacturing. We do not manufacture any of the components used in gas delivery systems and are therefore component neutral. This enables us to optimize overall designs for our customers by recommending the best available components on the basis of technology, performance and cost for incorporation into their gas delivery systems. Our component neutral position also enables us to maintain close relationships with a wide range of component suppliers who view us solely as a customer rather than as a competitor.

      Component testing capabilities. We have made significant investments in advanced analytic and automated test equipment and utilize our engineering expertise to test key components that we incorporate into our gas delivery systems. With our component testing capabilities, we can perform diagnostic tests,

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Our Strategy

      Our objective is to be the leading supplier of advanced gas delivery systems that are critical to the semiconductor manufacturing process. Our strategy is comprised of the following key elements:

      Increase our market share at existing customers. We believe that a significant market opportunity exists to grow our business with sales to our existing customers by gaining market share from our competitors and by obtaining new business in different product families as our customers continue to outsource their gas delivery system requirements.

      Broaden our customer base by expanding our resources and geographical presence. We plan to continue to attract new customers by promoting both the merits of outsourcing by leading OEMs and our own proven ability to meet the demands of OEMs. As we grow our business, we plan to increase our design, engineering and manufacturing capabilities. We believe significant growth opportunities exist in Europe and Asia.

      Drive profitable growth with our flexible cost structure. In response to changes in demand for our products, we undertake cost containment initiatives and benefit from our supply chain efficiencies. We believe that we are well positioned to respond to an upturn in our business without significant new capital investment. In addition, we believe we can add additional manufacturing personnel and test equipment to meet increased demand.

      Expand into new product markets using our existing expertise. We are committed to expanding beyond gas delivery systems into new product markets such as liquid delivery systems, catalytic steam generation systems and frame assemblies.

      Selectively pursue strategic acquisitions. We plan to accelerate the growth of our business by selectively pursuing strategic acquisitions that will enable us to expand our geographic reach, secure new customers, diversify into complementary product markets and broaden our technological capabilities and product offerings.

Risks Associated With Our Business

      Our business is subject to numerous risks, which are highlighted in the section entitled “Risk Factors” immediately following this prospectus summary, including:

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Our History

      Our business dates back to 1991 when Mitsubishi Corporation founded Ultra Clean Technology Systems and Service, Inc. Our business was operated as a subsidiary of Mitsubishi until November 2002. It was then acquired by Ultra Clean Holdings, Inc., which we refer to as the Ultra Clean acquisition. Ultra Clean Holdings, Inc. is owned by FP-Ultra Clean LLC (95.2%), a wholly-owned subsidiary of Francisco Partners, L.P., and by some of our key employees (4.8%). After completion of this offering, FP-Ultra Clean, LLC will own approximately 60.0% of our outstanding common stock, assuming no exercise of the underwriters’ over-allotment option. We conduct our operating activities primarily through Ultra Clean Technology Systems and Service, Inc., our wholly-owned subsidiary.

      Our principal executive offices are located at 150 Independence Drive, Menlo Park, California 94025 and our telephone number is (650) 323-4100. We maintain a web site at www.uct.com. The information on our web site is not part of this prospectus.

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THE OFFERING

      The common stock outstanding immediately after the offering is based on 10,245,395 shares outstanding as of December 31, 2003, and excludes:

      Except as otherwise indicated, all information in this prospectus assumes:

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SUMMARY CONSOLIDATED FINANCIAL INFORMATION

      The following table presents our summary consolidated financial information. You should read this information together with the “Selected Consolidated Financial Information,” our consolidated financial statements and related notes and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” included elsewhere in this prospectus. Ultra Clean Holdings, Inc. (Ultra Clean) was incorporated in October 2002 for the purpose of acquiring Ultra Clean Technology Systems and Service, Inc. (Predecessor) from Mitsubishi and did not have any significant operations prior to the Ultra Clean acquisition on November 15, 2002. Summary financial data for the periods prior to the Ultra Clean acquisition on November 15, 2002 are derived from the financial statements of Predecessor. The following financial information may not be indicative of our future performance.

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      The preceding table presents a summary of our balance sheet data as of December 31, 2003:

See note 1 of our consolidated financial statements for an explanation of the determination of the number of shares used in computing per share data.

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RISK FACTORS

      You should carefully consider the risks and uncertainties described below before making an investment decision. If any of the events or circumstances described below actually occur, our business, financial condition and results of operations could suffer, the trading price of our common stock could decline and you may lose part or all of your investment.

Risks Related to Our Business

The highly cyclical nature of the semiconductor industry and general economic slowdowns could harm our operating results.

      Our business and operating results depend in significant part upon capital expenditures by manufacturers of semiconductors, which in turn depend upon the current and anticipated market demand for semiconductors. Historically, the semiconductor industry has been highly cyclical, with recurring periods of over-supply of semiconductor products that have had a severe negative effect on the demand for capital equipment used to manufacture semiconductors. During these periods, we have experienced significant fluctuations in customer orders for our products. Our sales were $76.5 million in 2001, $84.3 million in 2002 and $77.5 million in 2003. Historically, semiconductor industry slowdowns have had, and future slowdowns may have, a material adverse effect on our operating results.

      In addition, the uncertainty regarding the growth rate of economies throughout the world has caused companies to reduce capital investment and may cause further reduction of such investments. These reductions have been particularly severe in the semiconductor capital equipment industry. A potential rebound in the worldwide economy in the near future will not necessarily mean that our business will experience similar effects. Moreover, if the worldwide economy does not rebound in the near future, our business may be further harmed.

Our quarterly revenue and operating results fluctuate significantly from period to period and this may cause volatility in our common stock price.

      Our quarterly revenue and operating results have fluctuated significantly in the past and we expect them to continue to fluctuate in the future for a variety of reasons, including:

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      As a result of the foregoing, we believe that quarter-to-quarter comparisons of our revenue and operating results may not be meaningful, and that these comparisons may not be an accurate indicator of our future performance. Changes in the timing or terms of a small number of transactions could disproportionately affect our operating results in any particular quarter. Moreover, our operating results in one or more future quarters may fail to meet the expectations of securities analysts or investors. If this occurs, we would expect to experience an immediate and significant decline in the trading price of our common stock.

We rely on a small number of customers for a significant portion of our sales, and any impairment of our relationships with these customers would adversely affect our business.

      A relatively small number of OEM customers have historically accounted for a significant portion of our sales, and we expect this trend to continue. Applied Materials, Inc. and Novellus Systems, Inc. together accounted for 91% of our sales in 2001. Applied Materials, Inc., Novellus Systems, Inc. and Lam Research Corporation as a group accounted for 98% of our sales in 2002 and 92% of our sales in 2003. Because of the small number of OEMs in our industry, most of whom are already our customers, it would be difficult to replace lost revenue resulting from the loss of, or the reduction, cancellation or delay in purchase orders by, any one of these customers. Consolidation among our customers may further concentrate our business in a limited number of customers and expose us to increased risks relating to dependence on a small number of customers. In addition, any significant pricing pressure exerted by a key customer could adversely effect our operating results.

      We have had to qualify, and are required to maintain our status, as a supplier for each of our customers. This is a lengthy process that involves the inspection and approval by a customer of our engineering, documentation, manufacturing and quality control procedures before that customer will place volume orders. Attempts to lessen the adverse effect of any loss of or reduction in sales to an existing customer through the rapid addition of one or more new customers would be difficult because of these qualification requirements. Consequently, our business, operating results and financial condition would be adversely affected by the loss of, or any reduction in orders by, any of our significant customers.

Because we are subject to order and shipment uncertainties, any significant reductions, cancellations or delays in customer orders could cause our revenue to decline and our operating results to suffer.

      Our revenue is difficult to forecast because we generally do not have a material backlog of unfilled orders and because of the short time frame within which we are often required to design, produce and deliver products to our customers. Most of our revenue in any quarter depends on customer orders for our products that we receive and fulfill in the same quarter. We do not have long-term purchase orders or contracts that contain minimum purchase commitments from our customers. Instead, we receive non-binding forecasts of the future volume of orders from our customers. At times, we order and build component inventory in advance of the receipt of actual customer orders. Customers may cancel order forecasts, change production quantities from forecasted volumes or delay production for reasons beyond our control. Furthermore, reductions, cancellations or delays in customer order forecasts occur without penalty to or compensation from the customer. Reductions, cancellations or delays in forecasted orders could cause us to hold inventory for longer than anticipated, which could reduce our gross profit, restrict our ability to fund our operations and cause us to incur unanticipated reductions or delays in revenue. If we do not obtain orders as we anticipate, we could have excess component inventory for a specific product that we would not be able to sell to another customer, likely resulting in inventory write-offs, which could have a material adverse affect on our business, financial condition and operating results. In addition, because many of our costs are fixed in the short-term, we could experience deterioration in our gross profit when our production volumes decline.

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The manufacturing of our products is highly complex, and if we are not able to effectively manage our manufacturing and procurement process, our business and operating results would suffer.

      The manufacturing of our products is a highly complex process that involves the integration of multiple components and requires effective management of our supply chain while meeting our customers’ design-to-delivery cycle time requirements. Through the course of the manufacturing process, our customers may modify design and system configurations in response to changes in their own customers’ requirements. In order to rapidly respond to these modifications and deliver our products to our customers in a timely manner, we must effectively manage our manufacturing and procurement process. If we fail to effectively manage this process, we risk losing customers and damaging our reputation which could limit our growth and have a material adverse affect on our business, financial condition and operating results.

OEMs may not continue to outsource subsystem manufacturing for their capital equipment which could adversely impact our operating results.

      The success of our business depends on OEMs continuing to outsource the manufacturing of gas delivery systems for their semiconductor capital equipment. Most of the largest OEMs have already outsourced a significant portion of their gas delivery systems. If OEMs do not continue to outsource gas delivery systems for their capital equipment, our revenue would be reduced, which could have a material adverse affect on our business, financial condition and operating results. In addition, if we are unable to obtain additional business as OEMs outsource their production of gas delivery systems, our business, financial condition and operating results could be adversely affected.

We may experience a variety of difficulties and incur a variety of costs as a result of acquisitions of companies or technologies, and the anticipated benefits of any such acquisitions may never be realized.

      We may make acquisitions of, or significant investments in, complementary companies or technologies, although no acquisitions or investments are currently pending. Any future acquisitions would be accompanied by risks such as:

      We may not be able to successfully integrate any business, products, technologies or personnel that we might acquire in the future, and our failure to do so could have a material adverse affect on our business, financial condition and operating results.

If we do not keep pace with developments in the semiconductor industry, and with technological innovation generally, our products may not be competitive.

      Rapid technological innovation in semiconductor manufacturing processes requires the semiconductor capital equipment industry to anticipate and respond quickly to evolving customer requirements and could

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      The timely development of new or enhanced products is a complex and uncertain process which requires that we:

The industry in which we participate is highly competitive and rapidly evolving, and if we are unable to compete effectively, our operating results would be harmed.

      Our industry is highly competitive and rapidly evolving. Our competitors are primarily companies that design and manufacture gas delivery systems for semiconductor capital equipment. Although we have not faced competition in the past from the largest subsystem and component manufacturers in the semiconductor capital equipment industry, these suppliers could compete with us in the future. Increased competition has in the past resulted, and could in the future result, in price reductions, reduced gross margins or loss of market share, any of which would harm our operating results. We are currently experiencing pricing pressure as we attempt to increase market share with our existing customers. Competitors may introduce new products for the markets currently served by our products. These products may have better performance, lower prices and achieve broader market acceptance than our products. Further, OEMs typically own the design rights to their products and may provide these designs to subsystem manufacturers. If our competitors obtain proprietary rights to these designs such that we are unable to obtain the designs necessary to manufacture products for our OEM customers, our business, financial condition and operating results could be adversely affected.

      Our competitors may have greater financial, technical, manufacturing and marketing resources than we do. As a result, they may be able to respond more quickly to new or emerging technologies and changes in customer requirements, devote greater resources to the development, promotion, sale and support of their products, and reduce prices to increase market share. Moreover, there may be merger and acquisition activity among our competitors and potential competitors that may provide our competitors and potential competitors with an advantage over us by enabling them to expand their product offerings and service capabilities to meet a broader range of customer needs. Further, if one of our customers develops or acquires the internal capability to develop and produce gas delivery systems, the loss of that customer could have a material adverse affect on our business, financial condition and operating results. The introduction of new technologies and new market entrants may also increase competitive pressures.

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We must achieve design wins to retain our existing customers and to obtain new customers.

      New semiconductor capital equipment typically has a lifespan of several years, and OEMs frequently specify which systems, subassemblies, components and instruments are to be used in their equipment. Once a specific system, subassembly, component or instrument is incorporated into a piece of semiconductor capital equipment, it will likely continue to be incorporated into that piece of equipment for a period of at least several months before the OEM uses the product of another supplier. Accordingly, it is important that our products are designed into the new semiconductor capital equipment of OEMs, which we refer to as a design win, in order to retain our competitive position with existing customers and to obtain new customers.

      We incur technology development and sales expenses with no assurance that our products will ultimately be designed into an OEM’s semiconductor capital equipment. Further, developing new customer relationships, as well as increasing our market share at existing customers, requires a substantial investment of our sales, engineering and management resources without any assurance from prospective customers that they will place significant orders. We believe that OEMs often select their suppliers and place orders based on long-term relationships. Accordingly, we may have difficulty achieving design wins from OEMs that are not currently our customers. Our operating results and potential growth could be adversely affected if we fail to achieve design wins with leading OEMs.

We have experienced significant growth in our business in recent periods, and we may not be able to manage our future growth successfully.

      Our ability to successfully execute our business plan in a rapidly evolving market requires an effective planning and management process. We have increased, and plan to continue to increase, the scope of our operations. Due to the cyclical nature of the semiconductor industry, however, future growth is difficult to predict. Future expansion efforts could be expensive and may strain our managerial and other resources. To manage future growth effectively, we must maintain and enhance our financial and operating systems and controls and manage expanded operations. The number of people we employ has grown and we expect this number to continue to grow in the near term. As of December 31, 2001 we had 130 employees, as of December 31, 2003 we had 231 employees, and as of February 23, 2004 we had 286 employees. The addition and training of new employees may lead to short-term quality control problems and place increased demands on our management and experienced personnel. If we do not manage growth properly, our business, operating results and financial condition would be adversely affected.

We will incur increased costs as a result of being a public company.

      We will face increased legal, accounting, administrative and other costs and expenses as a public company that we did not incur as a private company. The Sarbanes-Oxley Act of 2002, as well as new rules subsequently implemented by the Securities and Exchange Commission, the Public Company Accounting Oversight Board and The Nasdaq National Market, have required changes in the corporate governance practices of public companies. We expect these new rules and regulations to increase our legal and financial compliance costs and to make legal, accounting and administrative activities more time-consuming and costly. For example, as a result of becoming a public company, we plan to add two additional independent directors, create additional committees of our board of directors and adopt policies regarding internal controls and disclosure controls and procedures. We also expect to incur substantially higher costs to obtain directors and officers insurance. We cannot estimate the amount of additional costs we may incur or the timing of such costs.

We may not be able to respond quickly enough to increases in demand for our products.

      Demand shifts in the semiconductor industry are rapid and difficult to predict, and we may not be able to respond quickly enough to an increase in demand. Our ability to increase sales of our products depends, in part, upon our ability to:

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      If we are unable to respond to rapid increases in demand for our products on a timely basis or to manage any corresponding expansion of our manufacturing capacity effectively, our customers could increase their purchases from our competitors, which would adversely affect our business.

Our dependence on our suppliers may prevent us from delivering an acceptable product on a timely basis.

      We rely on both single source and sole source suppliers, some of whom are relatively small in size, for many of the components we use in our products. In addition, our customers often specify components made by particular suppliers that we must incorporate into their products. Our suppliers are under no obligation to provide us with components. As a result, the loss of or failure to perform by any of these providers could adversely affect our business and operating results. In addition, the manufacturing of certain components and subassemblies is an extremely complex process. Therefore, if a supplier was unable to provide the volume of components we require on a timely basis and at acceptable prices, we would have to identify and qualify replacements from alternative sources of supply. The process of qualifying new suppliers for these complex components is lengthy and could delay our production and adversely affect our business, operating results and financial condition. We may also experience difficulty in obtaining sufficient supply of components and raw materials in times of significant growth in our business. For example, we have recently experienced shortages in supplies of various components, such as mass flow controllers, valves and regulators, and certain prefabricated parts, such as sheet metal enclosures, used in the manufacture of our products. In addition, one of our competitors manufactures mass flow controllers that may be specified by one or more of our customers. If we are unable to obtain these particular mass flow controllers from our competitor or convince a customer to select alternative mass flow controllers, we may be unable to meet that customer’s requirements.

The technology labor market is very competitive, and our business will suffer if we are unable to hire and retain key personnel.

      Our future success depends in part on the continued service of our key executive officers, as well as our research, engineering, sales, manufacturing and administrative personnel, most of whom are not subject to employment or non-competition agreements. In addition, competition for qualified personnel in the technology industry is intense, and we operate in geographic locations in which labor markets are particularly competitive. Our business is particularly dependent on expertise which only a very limited number of engineers possess. The loss of any of our key employees, including Clarence L. Granger, our Chief Executive Officer, Bruce Wier, our Vice President of Engineering, Deborah Hayward, our Vice President of Sales, and Sowmya Krishnan, our Vice President of Technology, or the failure to attract and retain new qualified employees, would adversely affect our business, operating results and financial condition.

Defects in our products could damage our reputation, decrease market acceptance of our products, cause the unintended release of hazardous materials and result in potentially costly litigation.

      A number of factors, including design flaws, material and component failures, contamination in the manufacturing environment, impurities in the materials used and unknown sensitivities to process conditions, such as temperature and humidity, as well as equipment failures, may cause our products to contain undetected errors or defects. Problems with our products may:

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      If any of our products contain defects or have reliability, quality or compatibility problems, our reputation might be damaged and customers might be reluctant to buy our products. We may also face a higher rate of product defects as we increase our production levels. Product defects could result in the loss of, or impair our ability to attract, customers. In addition, we may not find defects or failures in our products until after they are installed in a semiconductor manufacturer’s fabrication facility. We may have to invest significant capital and other resources to correct these problems. Our current or potential customers also might seek to recover from us any losses resulting from defects or failures in our products. Hazardous materials flow through and are controlled by our products and an unintended release of these materials could result in serious injury or death. Liability claims could require us to spend significant time and money in litigation or pay significant damages.

Our business is largely dependent on the know-how of our employees, and we generally do not have a protected intellectual property position.

      Our business is largely dependent upon our design, engineering, manufacturing and testing know-how. We rely on a combination of trade secrets and contractual confidentiality provisions, and to a much lesser extent, patents, copyrights and trademarks, to protect our proprietary rights. Accordingly, our intellectual property position is more vulnerable than it otherwise would be if it were protected by issued patents. If we fail to successfully protect our proprietary rights, our competitive position could suffer, which could harm our operating results. We may be required to spend significant resources to monitor and protect our proprietary rights. In addition, we may not be able to detect infringement of our proprietary rights and may lose our competitive position in the market if any such infringement occurs. In addition, competitors may design around our technology or develop competing technologies and know-how.

Third parties may claim we are infringing their intellectual property which could subject us to litigation or licensing expenses, and we may be prevented from selling our products if any such claims prove successful.

      While we are not aware of any claims by third parties that we are infringing their intellectual property rights, we may be subject to such claims in the future. In addition, we may be unaware of intellectual property rights of others that may be applicable to our products. Any litigation regarding patents or other intellectual property could be costly and time-consuming and divert our management and key personnel from our business operations. The complexity of the technology involved in our products and the uncertainty of intellectual property litigation increase these risks. Claims of intellectual property infringement may also require us to enter into costly license agreements. However, we may not be able to obtain licenses on terms acceptable to us, or at all. We also may be subject to significant damages or injunctions against the development and sale of certain of our products if any such claims prove successful.

Our historical financial information may not be representative of our results as a stand-alone entity.

      From 1991 through 2002, we operated as a subsidiary of Mitsubishi Corporation. During that period, Mitsubishi provided us with financing. Accordingly, the historical financial information included in this prospectus does not necessarily reflect what our financial position, operating results and cash flows will be in the future or what they would have been had we been a separate, stand-alone entity during the periods in which we were owned by Mitsubishi. Furthermore, as a stand-alone entity, we will need to obtain any required funding from third parties.

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We may not be able to fund our future capital requirements from our operations, and financing from other sources may not be available on favorable terms or at all.

      We made capital expenditures of $0.6 million in 2001, $1.8 million in 2002 and $0.5 million in 2003. The amount of our future capital requirements will depend on many factors, including:

      To the extent that existing cash, together with any cash from operations, are insufficient to fund our future activities, we may need to raise additional funds through public or private equity or debt financing. Future equity financings could be dilutive to holders of our common stock, and debt financings could involve covenants that restrict our business operations. If we cannot raise funds on acceptable terms, if and when needed, we may not be able to develop or enhance our products, take advantage of future opportunities, grow our business or respond to competitive pressures or unanticipated requirements, any of which could adversely affect our business, operating results and financial condition.

If environmental contamination were to occur in one of our manufacturing facilities, we could be subject to substantial liabilities.

      We use substances regulated under various federal, state and local environmental laws in our manufacturing facilities. Our failure or inability to comply with existing or future environmental laws could result in significant remediation liabilities, the imposition of fines or the suspension or termination of the production of our products. In addition, we may not be aware of all environmental laws or regulations that could subject us to liability.

If our facilities were to experience catastrophic loss due to natural disasters, our operations would be seriously harmed.

      Our facilities could be subject to a catastrophic loss caused by natural disasters, including fires and earthquakes. We have facilities in areas with above average seismic activity, such as our manufacturing and headquarters facilities in Menlo Park, California. If any of our facilities were to experience a catastrophic loss, it could disrupt our operations, delay production and shipments, reduce revenue and result in large expenses to repair or replace the facility. In addition, we have in the past experienced, and may in the future experience, extended power outages at our Menlo Park, California facilities. We do not carry insurance policies which cover potential losses caused by earthquakes or other natural disasters or power loss.

Threatened or actual terrorist attacks may negatively impact our business and cause our stock price to decline.

      Future threatened or actual terrorist attacks against United States targets or military or trade disruptions impacting our component suppliers may cause delays or loss of customer orders. More generally, any of these events could cause consumer confidence and spending to decrease or result in increased volatility in United States and worldwide financial markets. These events could also result in further economic recession in the United States or abroad. Any of these occurrences would have an adverse impact on our business, operating results and financial condition.

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Risks Related to Our Ownership by Francisco Partners

We will be controlled by FP-Ultra Clean, LLC as long as it owns a significant percentage of our common stock, and our other stockholders will be unable to affect the outcome of stockholder voting during such time.

      After the completion of this offering, Francisco Partners, through its membership interests in FP-Ultra Clean, LLC, will beneficially own approximately 60.0% of our outstanding common stock, or approximately 54.5% if the underwriters exercise in full their over-allotment option to purchase additional shares. Pursuant to a stockholder’s agreement, our principal stockholder, FP-Ultra Clean, LLC, which is controlled by Francisco Partners, has the right, to nominate for election a majority of the members of our board of directors for so long as it holds at least 25% of our outstanding common stock.

      The stockholder’s agreement also provides that our board of directors may not take certain significant actions without the approval of FP-Ultra Clean, LLC as long as it owns at least 25% of our outstanding common stock. These actions include:

Such power could have the effect of delaying, deterring or preventing a change of control, business combination or other transaction that might otherwise be beneficial to our stockholders. FP-Ultra Clean, LLC also is not prohibited from selling a controlling interest in us to a third party or a participant in our industry. For additional information regarding our relationship with FP-Ultra Clean, LLC, you should read the section of this prospectus entitled “Certain Relationships and Related Party Transactions.”

FP-Ultra Clean, LLC and its designees on our board of directors may have interests that conflict with our interests and the interests of our other stockholders.

      FP-Ultra Clean, LLC and its designees on our board of directors may have interests that conflict with, or are different from, our own and those of our other stockholders. Francisco Partners, which will be the beneficial holder of 60.0% of our outstanding common stock after completion of this offering, assuming no exercise of the underwriters’ over-allotment option, through its membership interests in FP-Ultra Clean, LLC, has invested in or acquired other businesses that are involved in the semiconductor industry and may invest in or acquire others in the future. Conflicts of interest between FP-Ultra Clean, LLC and us or our other stockholders may arise. Our amended and restated certificate of incorporation to be effective upon the completion of this offering does not contain any provisions designed to facilitate resolution of actual or

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Risks Related to the Securities Markets and Ownership of Our Common Stock

Future sales of our common stock by existing stockholders could depress our stock price.

      Sales of substantial amounts of our common stock by FP-Ultra Clean, LLC, or the perception that these sales might occur, may depress prevailing market prices of our common stock. All of our outstanding shares are subject to lock-up agreements with the underwriters as described in “Underwriting” that prohibit the resale of these shares for 180 days from the date of this prospectus, although the underwriters may release all or a portion of the shares subject to lock-up agreements at any time without notice. The shares owned by FP-Ultra Clean, LLC have the benefit of an agreement with us that provides for customary demand and piggyback registration rights. Upon expiration of the 180-day lock-up period, in addition to the shares owned by FP-Ultra Clean, LLC that may be sold under a registration statement, shares underlying exercisable options to purchase our common stock will be available for resale without restriction or further registration under the Securities Act.

Our securities have no prior trading history, and we cannot assure you that our stock price will not decline after the offering.

      Prior to this offering, there was no public market for our common stock, and an active public market for our common stock may not develop or be sustained after this offering. The market price of our common stock could be subject to significant fluctuations after this offering. Among the factors that could affect our stock price are:

      The stock markets in general, and the markets for technology stocks in particular, have experienced extreme volatility that has often been unrelated to the operating performance of particular companies. These broad market fluctuations may adversely affect the trading price of our common stock. In particular, we cannot assure you that you will be able to resell your shares at or above the initial public offering price, which will be determined by negotiations between the representatives of the underwriters and us.

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We have broad discretion in how we use a portion of the net proceeds of this offering, and we may not use these proceeds in a manner desired by our stockholders.

      We do not currently have a specific plan with respect to the use of a significant portion of the net proceeds of this offering and have not committed these proceeds to any particular purpose. After deducting the underwriting discount and estimated offering expenses, including a $2.0 million advisory fee payable to Francisco Partners, we expect to use the net proceeds to redeem $29.3 million of our Series A Senior Notes held by FP-Ultra Clean LLC and $1.3 million of our Series A Senior Notes held by some of our key employees, plus accrued interest. We plan to use the balance of the net proceeds of this offering primarily for working capital and general corporate purposes. Our management will have broad discretion with respect to the use of the net proceeds and investors will be relying on the judgment of our management regarding the application of these proceeds. Our management could spend these proceeds in ways which our stockholders may not desire or that do not yield a favorable return. You will not have the opportunity, as part of your investment in our common stock, to influence the manner in which the net proceeds of this offering are used.

Provisions of our charter documents could discourage potential acquisition proposals and could delay, deter or prevent a change in control.

      In addition to the provisions of our stockholder’s agreement with FP-Ultra Clean, LLC described above, the provisions of our amended and restated certificate of incorporation and by-laws to be effective on the completion of this offering could deter, delay or prevent a third party from acquiring us, even if doing so would benefit our stockholders. These provisions include:

You will incur immediate and substantial dilution.

      The initial public offering price is substantially higher than the net book value per share of our outstanding common stock. As a result, if you purchase shares in this offering, you will incur immediate and substantial dilution, which would have been $5.67 per share as of December 31, 2003. In addition, as of December 31, 2003, options to purchase a total of 1,055,250 shares of common stock were outstanding, at a weighted average exercise price of $1.00 per share. To the extent these options are exercised, you will incur further dilution. See “Dilution” for a more complete description of the dilution that you will incur.

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FORWARD-LOOKING STATEMENTS

      This prospectus contains forward-looking statements which reflect our current views with respect to future events and financial performance. In this prospectus, we use words such as “anticipates,” “believes,” “plans,” “expects,” “future,” “intends,” “may,” “will,” “should,” “estimates,” “predicts,” “potential,” “continue” and similar expressions to identify these forward-looking statements. This prospectus also contains forward-looking statements attributed to third parties relating to their estimates regarding the growth of our markets. All forward-looking statements address matters that involve risks and uncertainties. Accordingly, you should not rely on forward-looking statements in this prospectus, as there are or will be important factors that could cause our actual results, as well as those of the markets we serve, levels of activity, performance, achievements and prospects to differ materially from the results predicted or implied by these forward-looking statements. These risks, uncertainties and other factors include, among others, those identified in “Risk Factors,” “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and elsewhere in this prospectus. We undertake no obligation to publicly update or review any forward-looking statements, whether as a result of new information, future developments or otherwise.

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USE OF PROCEEDS

      We estimate that our net proceeds from this offering, after deducting the underwriting discount and estimated offering expenses, including a $2.0 million advisory fee payable to Francisco Partners, will be approximately $38.1 million, based on an assumed initial public offering price of $7.50 per share. We expect to use the net proceeds to redeem $29.3 million of our Series A Senior Notes held by FP-Ultra Clean, LLC and $1.3 million of our Series A Senior Notes held by some of our key employees, plus accrued interest. Our Series A Senior Notes bear interest at a rate of 5% per annum and mature on November 15, 2009. We intend to use the remainder of the net proceeds for working capital and general corporate purposes. We will have discretion in the use of a significant portion of the net proceeds we receive from this offering. Investors will be relying on the judgment of our management regarding the application of those net proceeds. In addition, any investments, capital expenditures, cash acquisitions or other application of our proceeds may not produce the anticipated results. Pending use of these proceeds as discussed above, we intend to invest these funds in short-term, interest-bearing investment-grade obligations. We will not receive proceeds from any exercise of the underwriters’ over-allotment option.

DIVIDEND POLICY

      We have not paid any cash dividends on our common stock since the Ultra Clean acquisition. We intend to retain any future earnings to fund the development and growth of our business and do not anticipate paying any cash dividends in the foreseeable future. Any determination to pay dividends in the future will be at the discretion of our board of directors and, under the terms of our stockholder’s agreement, will require the approval of FP-Ultra Clean, LLC for as long as it holds at least 25% of our common stock. In addition, our revolving credit facility prohibits us from paying cash dividends on our common stock.

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CAPITALIZATION

      The following table sets forth our long-term debt and capitalization as of December 31, 2003.

      Our capitalization is presented:

      You should read the information set forth below together with the “Selected Consolidated Financial Information,” our consolidated financial statements and the related notes and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” included elsewhere in this prospectus.

      The number of shares of common stock outstanding after this offering excludes: 1,055,250 shares subject to options outstanding as of December 31, 2003, at a weighted average exercise price of $1.00 per share; 62,500 shares of restricted common stock granted in March 2004 under our Amended and Restated 2003 Stock Incentive Plan; 1,999,677 shares available for future issuance under our Amended and Restated 2003 Stock Incentive Plan, 210,750 of which will be subject to options to be granted to our non-employee directors and some of our employees upon completion of this offering at an exercise price equal to the initial public offering price; and 555,343 shares reserved for issuance under our Employee Stock Purchase Plan.

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DILUTION

      If you invest in our common stock in this offering, your ownership interest will be diluted to the extent of the difference between the amount you pay per share for our common stock in this offering and the net tangible book value per share of our common stock immediately after this offering. Net tangible book value per share is determined by dividing our tangible net worth, which is equal to our total tangible assets less total liabilities, by the aggregate number of shares of common stock outstanding. Our net tangible book value as of December 31, 2003 was a deficit of approximately $7,284,000, or $0.71 per share of common stock. After giving effect to the sale by us of 6,000,000 shares of common stock in this offering at an assumed initial public offering price of $7.50 per share and after deducting the underwriting discount and estimated offering expenses, including a $2.0 million advisory fee payable to Francisco Partners, and the receipt and application of a portion of the net proceeds to repurchase our outstanding Series A Senior Notes as described under “Use of Proceeds,” our net tangible book value at December 31, 2003 would have been $29,804,000, or $1.83 per share. This represents an immediate increase in net tangible book value to existing stockholders of $2.54 per share and an immediate dilution to new investors of $5.67 per share. The following table illustrates this per share dilution:

      Assuming the initial public offering had occurred on December 31, 2003, the following tables set forth, as of December 31, 2003, the number of shares of common stock purchased from us, the total consideration paid and the average price per share paid by existing stockholders and by the new investors, at an assumed initial public offering price of $7.50 per share before deducting the underwriting discount and estimated offering expenses payable by us.

      The foregoing table includes 201,393 shares of common stock that were subject to our right of repurchase at December 31, 2003, at a weighted average price of $1.00 per share. The foregoing table assumes no exercise of the underwriters’ over-allotment option or outstanding stock options after December 31, 2003, no issuance of shares reserved under our Amended and Restated 2003 Stock Incentive Plan and no issuance of shares reserved under our Employee Stock Purchase Plan.

      If the underwriters’ over-allotment option is exercised in full, the number of shares held by existing stockholders would be reduced to 9,345,395 or approximately 57.5% of the total shares of common stock outstanding, and the number of shares held by new investors would be 6,900,000, or approximately 42.5% of the total shares of common stock outstanding.

      As of December 31, 2003, options to purchase a total of 1,055,250 shares of common stock were outstanding, at a weighted average exercise price of $1.00 per share. Since December 31, 2003, we have issued 62,500 shares of restricted common stock under our Amended and Restated 2003 Stock Incentive Plan. In addition, we intend to grant options to purchase 210,750 shares of common stock to our directors and some of our employees upon completion of this offering at a weighted average exercise price equal to the initial public offering price. If all of these options are exercised, and after taking into account the

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SELECTED CONSOLIDATED FINANCIAL DATA

      The following selected consolidated financial data should be read together with our consolidated financial statements and related notes and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” included elsewhere in this prospectus. This financial data includes the accounts of Ultra Clean Technology Systems and Service, Inc. (Predecessor) for the period from January 1, 2002 through November 15, 2002 and for the years ended December 31, 2001, 2000 and 1999 and the accounts of Ultra Clean Holdings, Inc. (Ultra Clean) for the period from November 16, 2002 through December 31, 2002 and for the year ended December 31, 2003. See note 1 of the consolidated financial statements for a description of the Ultra Clean acquisition. The selected consolidated balance sheet data as of December 31, 2002 and 2003 and the selected consolidated statements of operations data for the year ended December 31, 2003, the periods from January 1, 2002 through November 15, 2002 and November 16, 2002 through December 31, 2002 and the year ended December 31, 2001 have been derived from our audited consolidated financial statements which are included elsewhere in this prospectus. The selected consolidated balance sheet data as of December 31, 1999, 2000 and 2001 and the selected consolidated statements of operations data for the years ended December 31, 1999 and 2000 have been derived from our audited consolidated financial statements not included in this prospectus. Historical results are not necessarily indicative of the results to be expected in the future.

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