September 17, 2021

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

Dear Investor:

UBS Asset Management is pleased to provide you with this interim holdings report for Master Trust – Prime Master Fund (the “Master Fund”). Each of the funds in the UBS Select Prime series is a “feeder fund” that invests in individual money market securities through the Master Fund. Holdings are as of September 10, 2021. The UBS Select Prime series feeder funds are designated by the use of "Select Prime" as part of each feeder fund's name.

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 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 Select 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 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. 16-0922

Master Trust—Prime Master Fund Holdings | September 10, 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 ABN AMRO BANK 285,000,000.000 09/13/2021 4.08 ALBION CAPITAL CORP 33,684,000.000 10/20/2021 0.48 ANZ NATNL INT LMTD 31,000,000.000 12/21/2021 0.44 ANZ NATNL INT LMTD 31,000,000.000 11/29/2021 0.44 ANZ NATNL INT LMTD 22,000,000.000 11/10/2021 0.31 ASB FINANCE LTD. 67,000,000.000 11/24/2021 0.96 ASB FINANCE LTD. 39,000,000.000 04/06/2022 0.56 ASB FINANCE LTD. 35,000,000.000 03/25/2022 0.50 BANK OF AMERICA 235,000,000.000 12/31/2099 3.36 BANK OF MONTREAL- 19,000,000.000 07/13/2022 0.27 BANK OF NOVA SCOTIA/THE 41,000,000.000 06/02/2022 0.59 BANK OF NOVA SCOTIA/THE 24,750,000.000 04/07/2022 0.35 BANQUE ET CAISSE 71,000,000.000 03/01/2022 1.02 BARCLAYS BANK PLC REPO 200,000,000.000 09/13/2021 2.86 BARCLAYS BK PLC 63,000,000.000 11/23/2021 0.90 BARCLAYS BK PLC 54,700,000.000 12/14/2021 0.78 BARTON CAPITAL CORP. 20,000,000.000 09/13/2021 0.29 BEDFORD ROW FDG CORP 42,000,000.000 11/01/2021 0.60 BEDFORD ROW FDG CORP 40,000,000.000 10/25/2021 0.57 BNP TRI PARTY CP2 175,000,000.000 09/13/2021 2.50 BNP TRI PARTY CP2 50,000,000.000 09/13/2021 0.72 BNZ INTNL FDG LTD 47,000,000.000 11/15/2021 0.67

CAISSE DES DEPOTS ET 25,000,000.000 01/14/2022 0.36 CAN AST + CAN LTD JT 32,000,000.000 10/04/2021 0.46 CAN AST + CAN LTD JT 30,000,000.000 10/04/2021 0.43 CANADIAN IMPERIAL BK 80,000,000.000 09/15/2021 1.14 CANADIAN IMPERIAL BK 65,000,000.000 09/17/2021 0.93 CANADIAN IMPERIAL BK 37,000,000.000 04/04/2022 0.53 COLLATERALIZED CP FLEX 35,000,000.000 10/19/2021 0.50 COLLATERALIZED CP V CO 13,000,000.000 10/04/2021 0.19 COOPERATIEVE CENTRALE 50,000,000.000 12/21/2021 0.72 CORPOERATIVE CENTRALE 29,000,000.000 05/06/2022 0.41 CREDIT AGRICOLE CIB 138,000,000.000 09/13/2021 1.97 CREDIT IND ET CM NY 125,000,000.000 09/13/2021 1.79 CREDIT IND ET CM NY 100,000,000.000 09/15/2021 1.43 DBS BANK LTD 44,000,000.000 10/20/2021 0.63 DBS BANK LTD 40,000,000.000 10/01/2021 0.57 DBS BANK LTD 40,000,000.000 11/15/2021 0.57 DBS BANK LTD 36,000,000.000 11/18/2021 0.51 DEXIA CREDIT LOCAL SA 65,000,000.000 03/17/2022 0.93 DEXIA CREDIT LOCAL SA 49,000,000.000 12/01/2021 0.70 DEXIA CREDIT LOCAL SA 35,000,000.000 11/02/2021 0.50 DZ BANK AG DEUTSCHE -Z 200,000,000.000 09/13/2021 2.86 ERSTE FINANCE LLC 128,000,000.000 09/16/2021 1.83 ERSTE FINANCE LLC 90,000,000.000 09/17/2021 1.29 EVERGREEN JOINT REPO 50,000,000.000 12/31/2099 0.72 FAIRWAY FINANCE CORP 44,000,000.000 09/16/2021 0.63 FAIRWAY FINANCE CORP 44,000,000.000 11/05/2021 0.63 FAIRWAY FINANCE CORP 26,000,000.000 02/24/2022 0.37 FAIRWAY FINANCE CORP 22,000,000.000 10/08/2021 0.31 FAIRWAY FINANCE CORP 15,000,000.000 02/02/2022 0.21 FEDERATION DES CAISSES 60,000,000.000 09/17/2021 0.86 FIXED INC CLEARING CORP.REPO 135,500,000.000 09/13/2021 1.94 J.P. MORGAN SECURITIES L 75,000,000.000 12/31/2099 1.07 J.P. MORGAN SECURITIES LLC 174,000,000.000 12/31/2099 2.49 LMA SA LMA AMERICAS 42,000,000.000 10/07/2021 0.60 LMA SA LMA AMERICAS 40,000,000.000 11/30/2021 0.57 LMA SA LMA AMERICAS 36,000,000.000 02/04/2022 0.51 LMA SA LMA AMERICAS 23,000,000.000 02/10/2022 0.33 LMA SA LMA AMERICAS 20,300,000.000 02/14/2022 0.29

LMA SA LMA AMERICAS 20,000,000.000 11/08/2021 0.29 LMA SA LMA AMERICAS 19,000,000.000 10/08/2021 0.27 LMA SA LMA AMERICAS 6,000,000.000 11/10/2021 0.09 MERRILL, LYNCH, PIERCE, FENNER 200,000,000.000 09/13/2021 2.86 MITSUBISHI UFJ TR+BKG 34,000,000.000 11/02/2021 0.49 MIZUHO BANK LTD 30,000,000.000 12/13/2021 0.43 MIZUHO CORP BANK GRAND CAYMAN 190,000,000.000 09/13/2021 2.72 MUFG BK LTD N Y BRH DISC COML 45,000,000.000 10/05/2021 0.64 MUFG BK LTD N Y BRH DISC COML 35,000,000.000 01/18/2022 0.50 NATIONAL BK OF CANAD 39,000,000.000 03/25/2022 0.56 NATIONAL BK OF CANAD 36,000,000.000 02/14/2022 0.51 NATIONAL BK OF CANAD 21,000,000.000 05/20/2022 0.30 NATIONWIDE BLDG SOC 110,000,000.000 10/06/2021 1.57 NATIONWIDE BLDG SOC 50,000,000.000 10/05/2021 0.72 NATL AUSTRALIA BK LT 29,000,000.000 02/16/2022 0.41 NEDERLANDSE WTRSCHBNK 25,000,000.000 09/15/2021 0.36 NIEUW AMSTERDAM RECV 16,000,000.000 11/12/2021 0.23 NORDEA BK AB PUBL 25,000,000.000 12/14/2021 0.36 NORINCHUKIN BK 85,000,000.000 11/05/2021 1.22 NORINCHUKIN BK 85,000,000.000 11/22/2021 1.22 NORINCHUKIN BK 42,000,000.000 02/25/2022 0.60 NRW. BANK 80,000,000.000 09/17/2021 1.14 NRW. BANK 27,000,000.000 09/15/2021 0.39 NRW. BANK 25,000,000.000 09/14/2021 0.36 OLD LINE FUNDING LLC 82,000,000.000 01/11/2022 1.17 OLD LINE FUNDING LLC 50,000,000.000 10/26/2021 0.72 OLD LINE FUNDING LLC 32,000,000.000 01/24/2022 0.46 OLD LINE FUNDING LLC 30,000,000.000 02/10/2022 0.43 OVERSEA-CHINESE BANKING CORP L 51,000,000.000 10/01/2021 0.73 ROYAL BK OF CANADA 32,000,000.000 12/16/2021 0.46 SHEFFIELD RECEIVABLE 25,000,000.000 11/15/2021 0.36 SKANDIN ENS BANKEN AG 45,000,000.000 11/18/2021 0.64 SKANDIN ENS BANKEN AG 45,000,000.000 10/05/2021 0.64 SKANDIN ENS BANKEN AG 40,000,000.000 02/11/2022 0.57 SKANDIN ENS BANKEN AG 35,000,000.000 04/01/2022 0.50 SOCIETE GENERALE 105,000,000.000 09/15/2021 1.50 SOCIETE GENERALE 30,000,000.000 09/14/2021 0.43 SUMITOMO MITSUI BKG CORP 40,000,000.000 11/18/2021 0.57

SUMITOMO MITSUI TR BK 80,000,000.000 09/24/2021 1.14 SUMITOMO MITSUI TR BK 30,000,000.000 12/23/2021 0.43 SUMITOMO MITSUI TRUST NY 55,000,000.000 11/17/2021 0.79 SUMITOMO MITSUI TRUST NY 23,000,000.000 11/10/2021 0.33 SUMITOMO MTSU BKG CORP 42,350,000.000 11/01/2021 0.61 SVENSKA HANDLSBNKN A 36,000,000.000 02/18/2022 0.51 SVENSKA HANDLSBNKN A 35,000,000.000 12/16/2021 0.50 SWEDBANK 33,000,000.000 02/23/2022 0.47 THUNDER BAY FNDNG LLC 47,000,000.000 03/04/2022 0.67 TORONTO DOMINION BANK 65,000,000.000 09/14/2021 0.93 TORONTO DOMINION BANK 45,000,000.000 05/05/2022 0.64 TORONTO DOMINION BANK 25,000,000.000 03/21/2022 0.36 TORONTO-DOMINION 28,000,000.000 12/09/2021 0.40 UNITED OVERSEAS BK LTD 65,000,000.000 09/27/2021 0.93 UNITED OVERSEAS BK LTD 44,000,000.000 05/03/2022 0.63 UNITED OVERSEAS BK LTD 43,000,000.000 02/07/2022 0.61 UNITED OVERSEAS BK LTD 35,000,000.000 06/01/2022 0.50 VERSAILLES CDS LLC 44,000,000.000 02/04/2022 0.63 VERSAILLES CDS LLC 43,000,000.000 03/01/2022 0.62 VICTORY RECEIVABLES 53,812,000.000 11/02/2021 0.77 VICTORY RECEIVABLES 48,600,000.000 12/08/2021 0.70 WESTPAC BANKING CORP. 45,000,000.000 12/01/2021 0.64 WESTPAC BANKING CORP. 45,000,000.000 11/24/2021 0.64

*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.