September 24, 2021

RE: Weekly update on the UBS Select ESG Prime series of funds.

Dear Investor:

UBS Asset Management is pleased to provide you with this interim holdings report for Master Trust– ESG Prime Master Fund (the “Master Fund”). Each of the funds in the UBS Select ESG Prime series is a “feeder fund” that invests in individual money market securities through the Master Fund. Holdings are as of September 17, 2021. The UBS Select ESG Prime series feeder funds are UBS Select ESG Prime Preferred Fund, UBS Select ESG Prime Institutional Fund and UBS Select ESG Prime Investor Fund.

Further information regarding portfolio holdings of the Master Fund is available on a monthly basis and through annual and semiannual reports. To view a copy of the Master Fund’s latest filing, you can visit the US Securities and Exchange Commission's website at http://www.sec.gov.

For more information, contact the UBS Asset Management National Sales Desk at 888-793 8637.

For the funds in the UBS Select ESG Prime series, investors should read and carefully consider the investment objectives, risks, charges and expenses before investing. The funds’ prospectuses contain this and other information about the funds. Contact the UBS Asset Management National Sales Desk at 888-793 8637 for a current fund prospectus. An investment in the funds in the UBS ESG Prime series is only one component of a balanced investment plan.

Investors should note that current and future portfolio holdings are subject to risk. You could lose money by investing in a UBS Select ESG Prime series fund. Because the share price of a fund will fluctuate, when you sell your shares they may be worth more or less than what you originally paid for them. The fund may impose a fee upon sale of your shares or may temporarily suspend your ability to sell shares if the fund's liquidity falls below required minimums because of market conditions or other factors. An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The fund's sponsor has no legal obligation to provide financial support to the fund, and you should not expect that the sponsor will provide financial support to the fund at any time. .

Not FDIC insured. May lose value. No bank guarantee.

UBS Asset Management (Americas) Inc. UBS Asset Management (US) Inc. is the funds’ distributor. AMMA-5154

Master Trust— ESG Prime Master Fund Holdings | September 17, 2021

Holdings and allocations shown are unaudited, and may not be representative of current or future investments. Holdings and allocations may not include the fund's entire investment portfolio, which may change at any time. Fund holdings should not be relied on in making investment decisions and should not be construed as research or investment advice regarding particular securities.

Please note: The fund is actively managed, and its holdings are subject to change.

Percent of Security name Par Maturity date* fund ALBION CAPITAL CORP 3,000,000.000 10/20/2021 0.33 ANZ NATNL INT LMTD 2,000,000.000 11/29/2021 0.22 ANZ NATNL INT LMTD 2,000,000.000 12/21/2021 0.22 ANZ NATNL INT LMTD 1,000,000.000 11/10/2021 0.11 ASB FINANCE LTD. 5,000,000.000 11/10/2021 0.54 ASB FINANCE LTD. 3,000,000.000 04/06/2022 0.33 ASB FINANCE LTD. 2,000,000.000 10/22/2021 0.22 ATLANTIC ASSET SECUR 1,500,000.000 09/20/2021 0.16 BANK OF MONTREAL- 3,000,000.000 06/23/2022 0.33 BANK OF NOVA SCOTIA/THE 5,000,000.000 09/16/2022 0.54 BANK OF NOVA SCOTIA/THE 3,000,000.000 06/02/2022 0.33 BANQUE ET CAISSE 10,350,000.000 10/01/2021 1.12 BANQUE ET CAISSE 4,000,000.000 03/09/2022 0.43 BANQUE ET CAISSE 4,000,000.000 03/01/2022 0.43 BANQUE ET CAISSE 2,000,000.000 10/01/2021 0.22 BARCLAYS BK PLC 8,000,000.000 11/12/2021 0.87 BARCLAYS BK PLC 8,000,000.000 11/23/2021 0.87 BARCLAYS BK PLC 6,000,000.000 12/14/2021 0.65 BARTON CAPITAL CORP. 15,000,000.000 09/20/2021 1.63 BEDFORD ROW FDG CORP 2,000,000.000 11/01/2021 0.22 BEDFORD ROW FDG CORP 1,500,000.000 01/03/2022 0.16 BEDFORD ROW FDG CORP 1,000,000.000 09/20/2021 0.11 BNZ INTNL FDG LTD 6,000,000.000 10/15/2021 0.65 CAN AST + CAN LTD JT 3,000,000.000 10/04/2021 0.33 CANADIAN IMPERIAL BK 5,000,000.000 09/23/2021 0.54

CANADIAN IMPERIAL BK 2,500,000.000 04/04/2022 0.27 CANADIAN IMPERIAL BK 2,500,000.000 05/04/2022 0.27 CHARIOT FNDG LLC 13,000,000.000 11/16/2021 1.41 COLLATERALIZED CP FLEX 2,000,000.000 04/08/2022 0.22 COLLATERALIZED CP FLEX 2,000,000.000 01/20/2022 0.22 COLLATERALIZED CP FLEX 2,000,000.000 10/13/2021 0.22 COLLATERALIZED CP V CO 2,500,000.000 10/04/2021 0.27 COLLATERIZED COML PAPER V CO L 2,000,000.000 02/22/2022 0.22 COOPERATIEVE CENTRALE 3,000,000.000 12/21/2021 0.33 CORPOERATIVE CENTRALE 3,000,000.000 11/10/2021 0.33 CORPOERATIVE CENTRALE 3,000,000.000 05/06/2022 0.33 CORPOERATIVE CENTRALE 2,500,000.000 11/29/2021 0.27 CREDIT AGRICOLE CIB 15,500,000.000 09/20/2021 1.68 CREDIT IND ET CM NY 15,000,000.000 09/20/2021 1.63 CREDIT IND ET CM NY 10,000,000.000 09/22/2021 1.09 DBS BANK LTD 8,000,000.000 09/20/2021 0.87 DBS BANK LTD 5,610,000.000 10/06/2021 0.61 DBS BANK LTD 3,000,000.000 02/01/2022 0.33 DBS BANK LTD 3,000,000.000 12/21/2021 0.33 DBS BANK LTD 2,500,000.000 11/15/2021 0.27 DBS BANK LTD 2,500,000.000 10/01/2021 0.27 DEXIA CREDIT LOCAL SA 8,000,000.000 03/17/2022 0.87 DEXIA CREDIT LOCAL SA 6,000,000.000 12/01/2021 0.65 ERSTE FINANCE LLC 27,000,000.000 09/23/2021 2.93 EVERGREEN JOINT REPO 1,000,000.000 12/31/2099 0.11 FAIRWAY FINANCE CORP 5,500,000.000 02/22/2022 0.60 FAIRWAY FINANCE CORP 5,000,000.000 04/12/2022 0.54 FAIRWAY FINANCE CORP 3,000,000.000 11/05/2021 0.33 FAIRWAY FINANCE CORP 2,750,000.000 11/15/2021 0.30 FAIRWAY FINANCE CORP 2,000,000.000 02/24/2022 0.22 FAIRWAY FINANCE CORP 1,000,000.000 10/08/2021 0.11 GOTHAM FDG CORP 10,000,000.000 01/05/2022 1.09 KFW 2,000,000.000 01/26/2022 0.22 KFW INTL FINANCE INC 8,000,000.000 10/01/2021 0.87 LIBERTY FUNDING LLC 6,500,000.000 10/07/2021 0.71 LIBERTY FUNDING LLC 5,000,000.000 11/08/2021 0.54 LMA SA LMA AMERICAS 4,000,000.000 02/04/2022 0.43 LMA SA LMA AMERICAS 3,000,000.000 02/10/2022 0.33

LMA SA LMA AMERICAS 3,000,000.000 10/05/2021 0.33 LMA SA LMA AMERICAS 2,000,000.000 11/30/2021 0.22 LMA SA LMA AMERICAS 1,750,000.000 11/10/2021 0.19 MANHATTAN ASSET FDG. 14,000,000.000 11/08/2021 1.52 MERRILL, LYNCH, PIERCE, FENNER 173,300,000.000 09/20/2021 18.83 MITSUBISHI UFJ TR+BKG 4,000,000.000 11/08/2021 0.43 MITSUBISHI UFJ TR+BKG 3,500,000.000 11/02/2021 0.38 MIZUHO CORP BANK GRAND CAYMAN 40,000,000.000 09/20/2021 4.35 MUFG BK LTD N Y BRH DISC COML 2,500,000.000 10/05/2021 0.27 NATIONAL BK OF CANAD 4,000,000.000 02/14/2022 0.43 NATIONAL BK OF CANAD 4,000,000.000 02/15/2022 0.43 NATIONAL BK OF CANAD 4,000,000.000 05/20/2022 0.43 NATIONAL BK OF CANAD 3,300,000.000 03/25/2022 0.36 NATIONWIDE BLDG SOC 14,000,000.000 10/12/2021 1.52 NATIONWIDE BLDG SOC 10,000,000.000 10/05/2021 1.09 NATL AUSTRALIA BK LT 10,000,000.000 10/01/2021 1.09 NATL AUSTRALIA BK LT 7,000,000.000 01/18/2022 0.76 NATL AUSTRALIA BK LT 3,000,000.000 02/16/2022 0.33 NIEUW AMSTERDAM RECV 12,000,000.000 11/12/2021 1.30 NIEUW AMSTERDAM RECV 10,000,000.000 10/12/2021 1.09 NIEUW AMSTERDAM RECV 4,000,000.000 11/12/2021 0.43 NORINCHUKIN BK 6,000,000.000 11/22/2021 0.65 NORINCHUKIN BK 5,000,000.000 11/29/2021 0.54 NORINCHUKIN BK 3,000,000.000 11/05/2021 0.33 NRW. BANK 23,000,000.000 09/24/2021 2.50 OLD LINE FUNDING LLC 4,000,000.000 02/23/2022 0.43 OLD LINE FUNDING LLC 3,000,000.000 01/24/2022 0.33 OLD LINE FUNDING LLC 2,500,000.000 11/01/2021 0.27 OLD LINE FUNDING LLC 2,000,000.000 01/11/2022 0.22 OVERSEA CHINESE BANKING 5,000,000.000 02/24/2022 0.54 OVERSEA-CHINESE BANKING CORP L 3,000,000.000 02/03/2022 0.33 OVERSEA-CHINESE BANKING CORP L 2,000,000.000 12/08/2021 0.22 OVERSEA-CHINESE BANKING CORP L 2,000,000.000 10/01/2021 0.22 ROYAL BK CDA 3,000,000.000 07/12/2022 0.33 ROYAL BK OF CANADA 2,000,000.000 12/16/2021 0.22 SHEFFIELD RECEIVABLE 9,000,000.000 12/16/2021 0.98 SHEFFIELD RECEIVABLE 6,000,000.000 12/13/2021 0.65 SHEFFIELD RECEIVABLE 3,000,000.000 11/15/2021 0.33

SKANDIN ENS BANKEN AG 6,000,000.000 11/12/2021 0.65 SKANDIN ENS BANKEN AG 5,750,000.000 10/06/2021 0.62 SKANDIN ENS BANKEN AG 3,000,000.000 12/20/2021 0.33 SKANDIN ENS BANKEN AG 3,000,000.000 11/09/2021 0.33 SKANDIN ENS BANKEN AG 2,500,000.000 12/10/2021 0.27 SKANDIN ENS BANKEN AG 2,000,000.000 01/05/2022 0.22 SKANDIN ENS BANKEN AG 1,000,000.000 02/11/2022 0.11 STARBIRD FDG. CORP 15,000,000.000 09/20/2021 1.63 SUMITOMO MITSUI BKG CORP 2,000,000.000 10/01/2021 0.22 SUMITOMO MITSUI TR BK 6,500,000.000 10/04/2021 0.71 SUMITOMO MITSUI TR BK 6,000,000.000 09/24/2021 0.65 SUMITOMO MITSUI TR BK 6,000,000.000 12/02/2021 0.65 SUMITOMO MITSUI TR BK 3,500,000.000 10/01/2021 0.38 SUMITOMO MITSUI TRUST NY 5,000,000.000 11/17/2021 0.54 SUMITOMO MTSU BKG CORP 7,000,000.000 10/15/2021 0.76 SUMITOMO MTSU BKG CORP 3,000,000.000 10/05/2021 0.33 SVENSKA HANDLSBNKN A 5,000,000.000 11/05/2021 0.54 SVENSKA HANDLSBNKN A 4,000,000.000 02/18/2022 0.43 SVENSKA HANDLSBNKN A 3,000,000.000 11/22/2021 0.33 SVENSKA HANDLSBNKN A 3,000,000.000 02/18/2022 0.33 SVENSKA HANDLSBNKN A 2,500,000.000 10/06/2021 0.27 SVENSKA HANDLSBNKN A 2,000,000.000 12/16/2021 0.22 SVENSKA HANDLSBNKN A 2,000,000.000 11/17/2021 0.22 SVENSKA HANDLSBNKN A 1,800,000.000 11/19/2021 0.20 SWEDBANK 4,000,000.000 02/23/2022 0.43 THUNDER BAY FNDNG LLC 5,000,000.000 01/10/2022 0.54 THUNDER BAY FNDNG LLC 5,000,000.000 03/04/2022 0.54 THUNDER BAY FNDNG LLC 2,000,000.000 10/18/2021 0.22 THUNDER BAY FNDNG LLC 2,000,000.000 11/01/2021 0.22 TORONTO DOMINION BANK 15,000,000.000 09/21/2021 1.63 TORONTO DOMINION BANK 3,000,000.000 05/05/2022 0.33 TORONTO DOMINION BANK 3,000,000.000 10/07/2021 0.33 TORONTO DOMINION BANK 2,000,000.000 12/16/2021 0.22 TORONTO-DOMINION 2,000,000.000 12/09/2021 0.22 UNITED OVERSEAS BK LTD 8,000,000.000 11/16/2021 0.87 UNITED OVERSEAS BK LTD 4,000,000.000 06/01/2022 0.43 UNITED OVERSEAS BK LTD 3,000,000.000 05/03/2022 0.33 UNITED OVERSEAS BK LTD 3,000,000.000 02/07/2022 0.33

UNITED OVERSEAS BK LTD 1,000,000.000 09/27/2021 0.11 VERSAILLES CDS LLC 2,000,000.000 02/04/2022 0.22 VICTORY RECEIVABLES 8,000,000.000 10/26/2021 0.87 VICTORY RECEIVABLES 5,000,000.000 11/02/2021 0.54 WESTPAC BANKING CORP. 4,500,000.000 09/07/2022 0.49 WESTPAC BANKING CORP. 2,000,000.000 11/15/2021 0.22 WESTPAC BANKING CORP. 2,000,000.000 11/18/2021 0.22 WESTPAC SECS NZ LTD 7,825,000.000 02/07/2022 0.85 WESTPAC SECS NZ LTD 2,000,000.000 11/15/2021 0.22

*In the case of certain securities (e.g., variable rate government securities), “deemed maturity” under Rule 2a-7 may be sooner than that indicated above because of the Rule’s maturity shortening provisions.