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U.S. Treasury Reserves Portfoliotrue
Semi-Annual Shareholder Report \| February 28, 2025

This semi-annual shareholder report contains important information about U.S. Treasury Reserves Portfolio for the period September 1, 2024, to February 28, 2025.
You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-masterfunds-documents. You can also request this information by contacting us at 1-800-625-4554, or 1-203-703-6002.

WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS? (based on a hypothetical $10,000 investment)


Fund Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment*^,†
U.S. Treasury Reserves Portfolio	$1	0.01%

*	Reflects fee waivers and/or expense reimbursements, without which expenses would have been higher. Additional amounts may be voluntarily waived and/or reimbursed from time to time.

†	Annualized.

KEY FUND STATISTICS (as of February 28, 2025)


Total Net Assets	$18,652,540,410
Total Number of Portfolio Holdings	58

WHAT DID THE FUND INVEST IN? (as of February 28, 2025)

Portfolio Composition (% of Total Investments)

Schedule of Investments (unaudited)

February 28, 2025

U.S. Treasury Reserves Portfolio

(Percentages shown based on Portfolio net assets)

Security	Rate	Maturity Date	Face Amount	Value
Short-Term Investments — 100.5%
U.S. Treasury Bills — 74.8%
U.S. Treasury Bills	3.293%	3/4/25	$763,350,000	$763,078,993 (a)
U.S. Treasury Bills	3.810%	3/6/25	448,200,000	447,924,584 (a)
U.S. Treasury Bills	4.006%	3/11/25	966,150,000	965,006,900 (a)
U.S. Treasury Bills	4.088%	3/13/25	589,320,000	588,479,585 (a)
U.S. Treasury Bills	4.186%	3/18/25	745,000,000	743,494,974 (a)
U.S. Treasury Bills	4.196%	3/20/25	824,700,000	822,844,690 (a)
U.S. Treasury Bills	4.224%	3/25/25	880,000,000	877,509,599 (a)
U.S. Treasury Bills	4.238%	3/27/25	450,000,000	448,620,519 (a)
U.S. Treasury Bills	4.143%	4/1/25	894,200,000	891,023,199 (a)
U.S. Treasury Bills	4.277%	4/3/25	642,350,000	639,849,199 (a)
U.S. Treasury Bills	4.300%	4/8/25	600,000,000	597,306,749 (a)
U.S. Treasury Bills	4.278%	4/10/25	672,000,000	668,845,489 (a)
U.S. Treasury Bills	4.302%	4/15/25	422,590,000	420,352,772 (a)
U.S. Treasury Bills	4.305%	4/17/25	500,000,000	497,236,139 (a)
U.S. Treasury Bills	4.312%	4/22/25	425,000,000	422,402,888 (a)
U.S. Treasury Bills	4.319%	4/24/25	500,000,000	496,824,500 (a)
U.S. Treasury Bills	4.103%	4/29/25	250,000,000	248,353,055 (a)
U.S. Treasury Bills	4.312%	5/1/25	300,000,000	297,856,527 (a)
U.S. Treasury Bills	4.332%	5/8/25	602,320,000	597,511,110 (a)
U.S. Treasury Bills	4.311%	5/13/25	140,000,000	138,807,236 (a)
U.S. Treasury Bills	4.337%	5/15/25	350,000,000	346,919,271 (a)
U.S. Treasury Bills	4.344%	5/22/25	300,000,000	297,112,917 (a)
U.S. Treasury Bills	4.358%	5/29/25	325,570,000	322,163,821 (a)
U.S. Treasury Bills	4.331%	6/3/25	50,000,000	49,451,275 (a)
U.S. Treasury Bills	4.441%	6/5/25	220,000,000	217,474,400 (a)
U.S. Treasury Bills	4.338%	6/10/25	120,000,000	118,584,317 (a)
U.S. Treasury Bills	4.334%	6/12/25	150,000,000	148,197,500 (a)
U.S. Treasury Bills	4.297%	6/20/25	130,080,000	128,411,507 (a)
U.S. Treasury Bills	4.339%	6/24/25	250,000,000	246,648,230 (a)
U.S. Treasury Bills	4.311%	6/26/25	100,000,000	98,644,750 (a)
U.S. Treasury Bills	4.236%	7/1/25	80,000,000	78,889,334 (a)(b)
U.S. Treasury Bills	4.333%	7/17/25	75,000,000	73,798,250 (a)
U.S. Treasury Bills	4.320%	7/24/25	100,000,000	98,322,430 (a)
U.S. Treasury Bills	4.351%	8/14/25	75,000,000	73,552,687 (a)
U.S. Treasury Bills	4.391%	8/21/25	75,000,000	73,479,042 (a)

Total U.S. Treasury Bills				13,944,978,438
U.S. Treasury Notes — 25.7%
U.S. Treasury Notes	0.375%	4/30/25	130,000,000	129,166,360

See Notes to Financial Statements.

U.S. Treasury Reserves Portfolio 2025 Semi-Annual Report

Schedule of Investments (unaudited) (cont’d)

February 28, 2025

U.S. Treasury Reserves Portfolio

(Percentages shown based on Portfolio net assets)

Security	Rate	Maturity Date	Face Amount	Value
U.S. Treasury Notes — continued
U.S. Treasury Notes	3.875%	4/30/25	$107,960,000	$107,793,126
U.S. Treasury Notes (3 mo. U.S. Treasury Money Market Yield + 0.169%)	4.424%	4/30/25	753,730,000	753,804,143 (c)
U.S. Treasury Notes	4.625%	6/30/25	80,000,000	79,914,800
U.S. Treasury Notes (3 mo. U.S. Treasury Money Market Yield + 0.125%)	4.380%	7/31/25	150,000,000	149,980,051 (c)
U.S. Treasury Notes	0.250%	9/30/25	157,000,000	153,341,991
U.S. Treasury Notes	5.000%	9/30/25	123,700,000	124,173,057
U.S. Treasury Notes	0.250%	10/31/25	141,800,000	138,039,838
U.S. Treasury Notes (3 mo. U.S. Treasury Money Market Yield + 0.170%)	4.425%	10/31/25	384,000,000	383,964,343 (c)
U.S. Treasury Notes	5.000%	10/31/25	45,000,000	45,174,453
U.S. Treasury Notes	4.875%	11/30/25	64,400,000	64,626,614
U.S. Treasury Notes	0.375%	12/31/25	137,000,000	132,686,208
U.S. Treasury Notes	4.250%	12/31/25	260,500,000	260,498,345
U.S. Treasury Notes	3.875%	1/15/26	85,100,000	84,823,007
U.S. Treasury Notes	4.250%	1/31/26	21,700,000	21,695,533
U.S. Treasury Notes (3 mo. U.S. Treasury Money Market Yield + 0.245%)	4.500%	1/31/26	849,000,000	850,298,792 (c)
U.S. Treasury Notes	1.625%	2/15/26	133,700,000	130,369,650
U.S. Treasury Notes	4.625%	2/28/26	67,250,000	67,506,086
U.S. Treasury Notes	0.750%	3/31/26	40,000,000	38,561,417
U.S. Treasury Notes	4.500%	3/31/26	31,000,000	31,101,465
U.S. Treasury Notes (3 mo. U.S. Treasury Money Market Yield + 0.150%)	4.405%	4/30/26	291,500,000	291,515,972 (c)
U.S. Treasury Notes (3 mo. U.S. Treasury Money Market Yield + 0.182%)	4.437%	7/31/26	240,000,000	240,004,900 (c)
U.S. Treasury Notes (3 mo. U.S. Treasury Money Market Yield + 0.205%)	4.460%	10/31/26	522,500,000	522,998,771 (c)

Total U.S. Treasury Notes				4,802,038,922
Total Investments — 100.5% (Cost — $18,747,017,360#)				18,747,017,360
Liabilities in Excess of Other Assets — (0.5)%				(94,476,950 )
Total Net Assets — 100.0%				$18,652,540,410

See Notes to Financial Statements.

U.S. Treasury Reserves Portfolio 2025 Semi-Annual Report

U.S. Treasury Reserves Portfolio

#	Aggregate cost for federal income tax purposes is substantially the same.
(a)	Rate shown represents yield-to-maturity.
(b)	Securities traded on a when-issued or delayed delivery basis.
(c)	Variable rate security. Interest rate disclosed is as of the most recent information available. Certain variable rate securities are not based on a published reference rate and spread but are determined by the issuer or agent and are based on current market conditions. These securities do not indicate a reference rate and spread in their description above.

See Notes to Financial Statements.

U.S. Treasury Reserves Portfolio 2025 Semi-Annual Report

Statement of Operations (unaudited)

For the Six Months Ended February 28, 2025

Investment Income:
Interest	$438,038,045
Expenses:
Investment management fee (Note 2)	9,334,942
Trustees’ fees	220,258
Legal fees	146,612
Fund accounting fees	119,631
Custody fees	51,196
Audit and tax fees	15,793
Miscellaneous expenses	51,284
Total Expenses	9,939,716
Less: Fee waivers and/or expense reimbursements (Note 2)	(9,334,942 )
Net Expenses	604,774
Net Investment Income	437,433,271
Net Realized Gain on Investments	220,328
Increase in Net Assets From Operations	$437,653,599

See Notes to Financial Statements.

U.S. Treasury Reserves Portfolio 2025 Semi-Annual Report

Statements of Changes in Net Assets

For the Six Months Ended February 28, 2025 (unaudited) and the Year Ended August 31, 2024	2025	2024
Operations:
Net investment income	$437,433,271	$882,540,095
Net realized gain	220,328	229,453
Increase in Net Assets From Operations	437,653,599	882,769,548
Capital Transactions:
Proceeds from contributions	42,152,574,000	71,048,881,907
Value of withdrawals	(40,949,171,596 )	(70,091,098,663 )
Increase in Net Assets From Capital Transactions	1,203,402,404	957,783,244
Increase in Net Assets	1,641,056,003	1,840,552,792
Net Assets:
Beginning of period	17,011,484,407	15,170,931,615
End of period	$18,652,540,410	$17,011,484,407

See Notes to Financial Statements.

U.S. Treasury Reserves Portfolio 2025 Semi-Annual Report

Financial Highlights

For the years ended August 31, unless otherwise noted:
	20251	2024	2023	2022	2021	2020
Net assets, end of period (millions)	$18,653	$17,011	$15,171	$17,407	$22,601	$18,141
Total return2	2.36 %	5.52 %	4.42 %	0.52 %	0.10 %	1.08 %
Ratios to average net assets:
Gross expenses	0.11 %3	0.11 %	0.11 %	0.11 %	0.11 %	0.11 %
Net expenses4,5	0.01 3	0.01	0.01	0.01	0.01	0.01
Net investment income	4.69 3	5.38	4.32	0.46	0.10	0.91

1	For the six months ended February 28, 2025 (unaudited).
2	Performance figures may reflect compensating balance arrangements, fee waivers and/or expense reimbursements. In the absence of compensating balance arrangements, fee waivers and/or expense reimbursements, the total return would have been lower. Past performance is no guarantee of future results. Total returns for periods of less than one year are not annualized.
3	Annualized.
4	The investment manager, pursuant to the terms of the feeder fund’s investment management agreement, has agreed to waive 0.10% of Portfolio expenses, attributable to the Portfolio’s investment management fee. Additional amounts may be voluntarily waived and/or reimbursed from time to time.
5	Reflects fee waivers and/or expense reimbursements.

See Notes to Financial Statements.

U.S. Treasury Reserves Portfolio 2025 Semi-Annual Report

Notes to Financial Statements (unaudited)

1. Organization and significant accounting policies

U.S. Treasury Reserves Portfolio (the “Portfolio”) is a separate diversified investment series of Master Portfolio Trust (the “Trust”). The Trust, a Maryland statutory trust, is registered under the Investment Company Act of 1940, as amended (the “1940 Act”), as an open-end management investment company. The Declaration of Trust permits the Board of Trustees (the “Board”) to issue beneficial interests in the Portfolio. At February 28, 2025, all investors in the Portfolio were funds advised or administered by the investment manager of the Portfolio and/or its affiliates.

The Portfolio follows the accounting and reporting guidance in Financial Accounting Standards Board (“FASB”) Accounting Standards Codification Topic 946, Financial Services – Investment Companies (“ASC 946”). The following are significant accounting policies consistently followed by the Portfolio and are in conformity with U.S. generally accepted accounting principles (“GAAP”), including, but not limited to, ASC 946. Estimates and assumptions are required to be made regarding assets, liabilities and changes in net assets resulting from operations when financial statements are prepared. Changes in the economic environment, financial markets and any other parameters used in determining these estimates could cause actual results to differ. Subsequent events have been evaluated through the date the financial statements were issued.

(a) Investment valuation. In accordance with Rule 2a-7 under the 1940 Act, money market instruments are valued at amortized cost, which approximates market value. This method involves valuing portfolio securities at their cost and thereafter assuming a constant amortization to maturity of any discount or premium. The Portfolio’s use of amortized cost is subject to its compliance with certain conditions as specified by Rule 2a-7 under the 1940 Act.

Pursuant to policies adopted by the Board, the Portfolio’s manager has been designated as the valuation designee and is responsible for the oversight of the daily valuation process. The Portfolio’s manager is assisted by the Global Fund Valuation Committee (the “Valuation Committee”). The Valuation Committee is responsible for making fair value determinations, evaluating the effectiveness of the Portfolio’s pricing policies, and reporting to the Board.

The Portfolio uses valuation techniques to measure fair value that are consistent with the market approach and/or income approach, depending on the type of security and the particular circumstance. The market approach uses prices and other relevant information generated by market transactions involving identical or comparable securities. The income approach uses valuation techniques to discount estimated future cash flows to present value.

U.S. Treasury Reserves Portfolio 2025 Semi-Annual Report

GAAP establishes a disclosure hierarchy that categorizes the inputs to valuation techniques used to value assets and liabilities at measurement date. These inputs are summarized in the three broad levels listed below:

•

Level 1 — unadjusted quoted prices in active markets for identical investments

•

Level 2 — other significant observable inputs (including quoted prices for similar investments, interest rates, prepayment speeds, credit risk, etc.)

•

Level 3 — significant unobservable inputs (including the Portfolio’s own assumptions in determining the fair value of investments)

The inputs or methodologies used to value securities are not necessarily an indication of the risk associated with investing in those securities.

The following is a summary of the inputs used in valuing the Portfolio’s assets carried at fair value:

ASSETS
Description	Quoted Prices (Level 1)	Other Significant Observable Inputs (Level 2)	Significant Unobservable Inputs (Level 3)	Total
Short-Term Investments†	—	$18,747,017,360	—	$18,747,017,360

†	See Schedule of Investments for additional detailed categorizations.

(b) Repurchase agreements. The Portfolio may enter into repurchase agreements with institutions that its subadviser has determined are creditworthy. Each repurchase agreement is recorded at cost. Under the terms of a typical repurchase agreement, the Portfolio acquires a debt security subject to an obligation of the seller to repurchase, and of the Portfolio to resell, the security at an agreed-upon price and time, thereby determining the yield during the Portfolio’s holding period. When entering into repurchase agreements, it is the Portfolio’s policy that its custodian or a third party custodian, acting on the Portfolio’s behalf, take possession of the underlying collateral securities, the market value of which, at all times, at least equals the principal amount of the repurchase transaction, including accrued interest. To the extent that any repurchase transaction maturity exceeds one business day, the value of the collateral is marked-to-market and measured against the value of the agreement in an effort to ensure the adequacy of the collateral. If the counterparty defaults, the Portfolio generally has the right to use the collateral to satisfy the terms of the repurchase transaction. However, if the market value of the collateral declines during the period in which the Portfolio seeks to assert its rights or if bankruptcy proceedings are commenced with respect to the seller of the security, realization of the collateral by the Portfolio may be delayed or limited.

(c) Securities traded on a when-issued and delayed delivery basis. The Portfolio may trade securities on a when-issued or delayed delivery basis. In when-issued and

U.S. Treasury Reserves Portfolio 2025 Semi-Annual Report

Notes to Financial Statements (unaudited) (cont’d)

delayed delivery transactions, the securities are purchased or sold by the Portfolio with payment and delivery taking place in the future in order to secure what is considered to be an advantageous price and yield to the Portfolio at the time of entering into the transaction.

Purchasing such securities involves risk of loss if the value of the securities declines prior to settlement. These securities are subject to market fluctuations and their current value is determined in the same manner as for other securities.

(d) Interest income and expenses. Interest income (including interest income from payment-in-kind securities) consists of interest accrued and discount earned (including both original issue and market discount adjusted for amortization of premium) on the investments of the Portfolio. Expenses of the Portfolio are accrued daily. The Portfolio bears all costs of its operations other than expenses specifically assumed by the investment manager.

(e) Method of allocation. Net investment income of the Portfolio is allocated pro rata, based on respective ownership interests, among the Fund and other investors in the Portfolio (the “Holders”) at the time of such determination. Gross realized gains and/or losses of the Portfolio are allocated to the Holders in a manner such that the net asset values per share of each Holder, after each such allocation, is closer to the total of all Holders’ net asset values divided by the aggregate number of shares outstanding for all Holders.

(f) Compensating balance arrangements. The Portfolio has an arrangement with its custodian bank whereby a portion of the custodian’s fees is paid indirectly by credits earned on the Portfolio’s cash on deposit with the bank.

(g) Income taxes. The Portfolio is classified as a partnership for federal income tax purposes. As such, each investor in the Portfolio is treated as owner of its proportionate share of the net assets, income, expenses and realized gains and losses of the Portfolio. Therefore, no federal income tax provision is required. It is intended that the Portfolio’s assets will be managed so an investor in the Portfolio can satisfy the requirements of Subchapter M of the Internal Revenue Code.

Management has analyzed the Portfolio’s tax positions taken on income tax returns for all open tax years and has concluded that as of August 31, 2024, no provision for income tax is required in the Portfolio’s financial statements. The Portfolio’s federal and state income tax returns for tax years for which the applicable statutes of limitations have not expired are subject to examination by the Internal Revenue Service and state departments of revenue.

(h) Other. Purchases, maturities and sales of money market instruments are accounted for on the date of the transaction. Realized gains and losses are calculated on the identified cost basis.

U.S. Treasury Reserves Portfolio 2025 Semi-Annual Report

2. Investment management agreement and other transactions with affiliates

Franklin Templeton Fund Adviser, LLC (“FTFA”) is the Portfolio’s investment manager and Western Asset Management Company, LLC (“Western Asset”) is the Portfolio’s subadviser. FTFA and Western Asset are indirect, wholly-owned subsidiaries of Franklin Resources, Inc. (“Franklin Resources”).

Under the investment management agreement, the Portfolio pays an investment management fee, calculated daily and paid monthly, at an annual rate of 0.10% of the Portfolio’s average daily net assets.

FTFA provides administrative and certain oversight services to the Portfolio. FTFA delegates to the subadviser the day-to-day portfolio management of the Portfolio. For its services, FTFA pays Western Asset a fee monthly, at an annual rate equal to 70% of the net management fee it receives from the Portfolio.

As a result of the investment management agreement between FTFA and the feeder fund, FTFA has agreed to waive 0.10% of Portfolio expenses, attributable to the Portfolio’s investment management fee. Additional amounts may be voluntarily waived and/or reimbursed from time to time.

During the six months ended February 28, 2025, fees waived and/or expenses reimbursed amounted to $9,334,942.

FTFA is permitted to recapture amounts waived and/or reimbursed to the Portfolio during the same fiscal year under certain circumstances.

All officers and one Trustee of the Trust are employees of Franklin Resources or its affiliates and do not receive compensation from the Trust.

3. Derivative instruments and hedging activities

During the six months ended February 28, 2025, the Portfolio did not invest in derivative instruments.

4. Operating segments

The Portfolio has adopted the Financial Accounting Standards Board (FASB) Accounting Standards Update (ASU) 2023-07, Segment Reporting (Topic 280) - Improvements to Reportable Segment Disclosures. The update is limited to disclosure requirements and does not impact the Portfolio’s financial position or results of operations.

The Portfolio operates as a single operating segment, which is an investment portfolio. The Portfolio’s Investment Manager serves as the Chief Operating Decision Maker (CODM), evaluating fund-wide results and performance under a unified investment strategy. The CODM uses these measures to assess fund performance and allocate resources effectively. Internal reporting provided to the CODM aligns with the accounting policies and measurement principles used in the financial statements.

U.S. Treasury Reserves Portfolio 2025 Semi-Annual Report

Notes to Financial Statements (unaudited) (cont’d)

For information regarding segment assets, segment profit or loss, and significant expenses, refer to the Statement of Assets and Liabilities and the Statement of Operations, along with the related Notes to Financial Statements. The Portfolio’s Schedule of Investments provides details of the Portfolio’s investments that generate returns such as interest, dividends, and realized and unrealized gains or losses. Performance metrics, including expense ratios, are disclosed in the Financial Highlights.

U.S. Treasury Reserves Portfolio 2025 Semi-Annual Report

The information is disclosed as part of the Financial Statements included in Item 7 of this Form N-CSR.

The information is disclosed as part of the Financial Statements included in Item 7 of this Form N-CSR, as applicable.

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, the registrant has duly caused this Report to be signed on its behalf by the undersigned, there unto duly authorized.

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, this report has been signed below by the following persons on behalf of the registrant and in the capacities and on the dates indicated.

Assets:
Investments, at value	$18,747,017,360
Cash	499,999,527
Interest receivable	21,286,277
Total Assets	19,268,303,164
Liabilities:
Payable for securities purchased	615,489,796
Trustees’ fees payable	12,038
Accrued expenses	260,920
Total Liabilities	615,762,754
Total Net Assets	$18,652,540,410
Represented by:
Paid-in capital	$18,652,540,410

Changes in and Disagreements with Accountants	For the period covered by this report
Not applicable.
Results of Meeting(s) of Shareholders	For the period covered by this report
Not applicable.
Remuneration Paid to Directors, Officers and Others	For the period covered by this report
Refer to the financial statements included herein.

Master Portfolio Trust

By:	/s/ Jane Trust
	Jane Trust
	Chief Executive Officer

Date:	April 21, 2025

By:	/s/ Jane Trust
	Jane Trust
	Chief Executive Officer

Date:	April 21, 2025

By:	/s/ Christopher Berarducci
	Christopher Berarducci
	Principal Financial Officer

Date:	April 21, 2025


	WHERE CAN I FIND ADDITIONAL INFORMATION ABOUT THE FUND?
	Additional information is available on https://www.franklintempleton.com/regulatory-masterfunds-documents, including its:
	• proxy voting information • financial information • holdings • tax information