Blackrock Financial Institutions Series Trust N-CSR Certified annual shareholder report (management investment company)

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-CSR

CERTIFIED SHAREHOLDER REPORT OF REGISTERED MANAGEMENT

INVESTMENT COMPANIES

Investment Company Act file number: 811-03189

Name of Fund: BlackRock Financial Institutions Series Trust

BlackRock Summit Cash Reserves Fund

Fund Address: 100 Bellevue Parkway, Wilmington, DE 19809

Name and address of agent for service: John M. Perlowski, Chief Executive Officer, BlackRock Financial Institutions Series Trust, 50 Hudson Yards, New York, NY 10001

Registrant’s telephone number, including area code: (800) 441-7762

Date of fiscal year end: 04/30/2023

Date of reporting period: 04/30/2023

Item 1 – Report to Stockholders

(a) The Report to Shareholders is attached herewith.

APRIL 30, 2023

2023 Annual Report

BlackRock Financial Institutions Series Trust

· BlackRock Summit Cash Reserves Fund

Not FDIC Insured • May Lose Value • No Bank Guarantee

The Markets in Review

Dear Shareholder,

Investors faced an uncertain economic landscape during the 12-month reporting period ended April 30, 2023, amid mixed indicators and rapidly changing market conditions. The U.S. economy returned to modest growth beginning in the third quarter of 2022, although the pace of growth slowed thereafter. Inflation was elevated, reaching a 40-year high as labor costs grew rapidly and unemployment rates reached the lowest levels in decades. However, inflation moderated as the period continued, while continued strength in consumer spending backstopped the economy.

Equity returns varied substantially, as large-capitalization U.S. stocks gained for the period amid a rebound in big tech stocks, whereas small-capitalization U.S. stocks declined. International equities from developed markets advanced strongly, while emerging market stocks declined, pressured by higher interest rates and volatile commodities prices.

The 10-year U.S. Treasury yield rose during the reporting period, driving its price down, as investors reacted to elevated inflation and attempted to anticipate future interest rate changes. The corporate bond market also faced inflationary headwinds, although high-yield corporate bonds posted a positive return as demand from yield-seeking investors remained strong.

The U.S. Federal Reserve (the “Fed”), acknowledging that inflation has been more persistent than expected, raised interest rates eight times. Furthermore, the Fed wound down its bond-buying programs and incrementally reduced its balance sheet by not replacing securities that reach maturity. In addition, the Fed added liquidity to markets amid the failure of prominent regional banks.

Restricted labor supply kept inflation elevated even as other inflation drivers, such as goods prices and energy costs, moderated. While economic growth was modest in the last year, we believe that stickiness in services inflation and continued wage growth will keep inflation above central bank targets for some time. Although the Fed has decelerated the pace of interest rate hikes and indicated a pause could be its next step, we believe that the Fed still seems determined to get inflation back to target. With this in mind, we believe the possibility of a U.S. recession in the near term is high, but the dimming economic outlook has not yet been fully reflected in current market prices. We believe investors should expect a period of higher volatility as markets adjust to the new economic reality and policymakers attempt to adapt to rapidly changing conditions. Turmoil in the banking sector late in the period highlighted the potential for the rapid increase in interest rates to disrupt markets with little warning.

While we favor an overweight to equities in the long term, we prefer an underweight stance on equities overall in the near term. Expectations for corporate earnings remain elevated, which seems inconsistent with the possibility of a recession. Nevertheless, we are overweight on emerging market stocks as we believe a weakening U.S. dollar could provide a supportive backdrop. We also see selective, long-term opportunities in credit, where we believe that valuations are appealing, and higher yields offer attractive income. However, we are neutral on credit in the near term, as we’re concerned about tightening credit and financial conditions. For fixed income investing with a six- to twelve-month horizon, we see the most significant opportunities in short-term U.S. Treasuries, global inflation-linked bonds, and emerging market bonds denominated in local currency.

Overall, our view is that investors need to think globally, position themselves to be prepared for a decarbonizing economy, and be nimble as market conditions change. We encourage you to talk with your financial advisor and visit blackrock.com for further insight about investing in today’s markets.

Sincerely,

Rob Kapito

President, BlackRock Advisors, LLC

Rob Kapito

President, BlackRock Advisors, LLC

Total Returns as of April 30, 2023
	6-Month	12-Month
U.S. large cap equities (S&P 500® Index)	8.63%	2.66%
U.S. small cap equities (Russell 2000® Index)	(3.45)	(3.65)
International equities (MSCI Europe, Australasia, Far East Index)	24.19	8.42
Emerging market equities (MSCI Emerging Markets Index)	16.36	(6.51)
3-month Treasury bills (ICE BofA 3-Month U.S. Treasury Bill Index)	2.09	2.83
U.S. Treasury securities (ICE BofA 10-Year U.S. Treasury Index)	7.14	(1.68)
U.S. investment grade bonds (Bloomberg U.S. Aggregate Bond Index)	6.91	(0.43)
Tax-exempt municipal bonds (Bloomberg Municipal Bond Index)	7.65	2.87
U.S. high yield bonds (Bloomberg U.S. Corporate High Yield 2% Issuer Capped Index)	6.21	1.21
Past performance is not an indication of future results. Index performance is shown for illustrative purposes only. You cannot invest directly in an index.

2 THIS  PAGE  IS  NOT  PART  OF  YOUR  FUND  REPORT

Table of Contents

	Page
The Markets in Review		2
Annual Report:
Money Market Overview		4
Fund Summary		5
Disclosure of Expenses		5
Financial Statements:
Schedule of Investments		6
Statement of Assets and Liabilities		8
Statement of Operations		10
Statements of Changes in Net Assets		11
Financial Highlights		12
Notes to Financial Statements		15
Report of Independent Registered Public Accounting Firm		20
Important Tax Information		21
Trustee and Officer Information		22
Additional Information		26
Glossary of Terms Used in this Report		28

3

Money Market Overview  For the 12-Month Period Ended April 30, 2023

Market Review

Economic conditions in the United States were challenging throughout most of 2022: the unemployment rate trended at low levels throughout 2022 (and remained strong 3.4% in April 2023). Headline consumer price index (“CPI”) hit a high of 9.1% in June of 2022 (the largest increase in over 40 years) but decreased to 4.9% by the end of April 2023 largely due to Fed intervention.

The strength of the labor market and spiraling price pressures in the United States prompted the Fed’s Federal Open Market Committee (the “FOMC” or “Committee”) to continue on the path of aggressive rate hikes for the remainder of the year and into 2023. From March through December 2022, the Fed hiked rates a total of 425 basis points (or 4.25%). This would prove to be the fastest pace of hikes in over four decades. Additionally, the Committee raised the target Federal Funds range to 4.75% - 5.00% with two 25 basis points (or 0.25%) rate hikes in February and March 2023.

The median federal funds rate forecast for 2023 (“dot plot”) contained in the Summary of Economic Projections released in conjunction with the March 22, 2023 FOMC meeting was unchanged from the projection of 5.10% at the December 14, 2022 meeting, implying an estimated one additional 0.25% increase in the range for the target rate during the balance of 2023. As was widely expected, the Committee noted it will continue reducing its holdings of Treasury securities, agency debt and agency mortgage-backed securities as delineated in its Plans for Reducing the Size of the Fed’s Balance Sheet released in conjunction with the May 4, 2022 FOMC meeting.

In a statement release in conjunction with the March 22, 2023 meeting, the Committee expressed concerns about “recent developments” in the U.S. banking system that “are likely to result in tighter credit conditions” and “weigh on economic activity, hiring, and inflation.” At the same time, the statement noted that the “U.S. banking system is sound and resilient.”

Daily utilization of the Fed’s Reverse Repurchase Program (“RRP”) facility surged following the first adjustment in the program’s offering rate in June 2021, averaging over $2.2 trillion per day for the reporting period ended April 30, 2023. On December 30, 2022, the RRP facility hit an all-time high with a balance of over $2.55 trillion.

The Secured Overnight Financing Rate (“SOFR”)– a broad measure of the cost of borrowing cash overnight collateralized by Treasuries – stood at 4.81% for the period ended April 30, 2023. As of April 28, 2023, Treasury bill (“T-bill”) tenors between one-month and one-year traded between 4.18% and 4.76%. For reference, T-bills of the same tenors traded between 0.27% and 1.98% as of April 28, 2022. Rates continuously trended higher in 2022 into early 2023 with persistently higher than expected inflation prints and market expectations of an increasingly hawkish Fed.

During the 12-month period, the Treasury General Account TGA at the Fed reached a high of $964 billion on May 4, 2022 and a low of $87 billion on April 12, 2023. As of April 26, 2023, the balance was approximately $296 billion as the “X-date” (when the Treasury Department’s ability to finance the operations of the federal government comes to an end) approaches.

Our view is that the FOMC will likely maintain a ‘higher-for-longer’ policy stance given still elevated inflation. While a slowing economy, moderating inflation and banking sector stress support a pause soon in this hiking cycle, we do not expect the cuts that the market is currently predicting given that inflation remains well above the FOMC’s 2% target.

The debt ceiling will be increasingly in focus as we approach the window for the “X-date.” The yields on Treasury bills deemed vulnerable to a delayed payment could experience meaningful increases relative to those maturing outside of the range. Treasury bill supply is expected to move meaningfully higher upon a resolution.

Past performance is not an indication of future results. Index performance is shown for illustrative purposes only. You cannot invest directly in an index.

4 2 0 2 3   BLACK ROCK  ANNUAL  REPORT   TO  SHAREHOLDERS

Fund Summary  as of April 30, 2023 BlackRock Summit Cash Reserves Fund

Investment Objective

BlackRock Summit Cash Reserves Fund’s (the “Fund”) investment objective is to seek current income, preservation of capital and liquidity available from investing in a diversified portfolio of short-term money market securities.

CURRENT SEVEN-DAY YIELDS

	7-Day SEC Yield			7-Day Yield
Institutional		4.46	%		4.46	%
Investor A		4.46			4.46
Investor C		3.71			3.71

The 7-Day SEC Yield may differ from the 7-Day Yield shown above due to the fact that the 7-Day SEC Yield excludes distributed capital gains.

Past performance is not indicative of future results.

PORTFOLIO ALLOCATION

Asset Type	Percent of Net Assets
Repurchase Agreements		62.1	%
U.S. Government Sponsored Agency Securities		38.4
U.S. Treasury Obligations		1.9
Liabilities in Excess of Other Assets		(2.4	)

Disclosure of Expenses

Shareholders of the Fund may incur the following charges: (a) transactional expenses, such as sales charges; and (b) operating expenses, including investment advisory fees, service and distribution fees, and other fund expenses. The expense example shown (which is based on a hypothetical investment of $1,000 invested at the beginning of the period and held through the end of the period) is intended to assist shareholders both in calculating expenses based on an investment in the Fund and in comparing these expenses with similar costs of investing in other mutual funds.

The expense example provides information about actual account values and actual expenses. Annualized expense ratios reflect contractual and voluntary fee waivers, if any. In order to estimate the expenses a shareholder paid during the period covered by this report, shareholders can divide their account value by $1,000 and then multiply the result by the number corresponding to their share class under the heading entitled “Expenses Paid During the Period.”

The expense example also provides information about hypothetical account values and hypothetical expenses based on the Fund’s actual expense ratio and an assumed rate of return of 5% per year before expenses. In order to assist shareholders in comparing the ongoing expenses of investing in the Fund and other funds, compare the 5% hypothetical example with the 5% hypothetical examples that appear in shareholder reports of other funds.

The expenses shown in the expense example are intended to highlight shareholders’ ongoing costs only and do not reflect transactional expenses, such as sales charges, if any. Therefore, the hypothetical example is useful in comparing ongoing expenses only and will not help shareholders determine the relative total expenses of owning different funds. If these transactional expenses were included, shareholder expenses would have been higher.

Expense Example

	Actual							Hypothetical 5% Return
		Beginning Account Value (11/01/22)		Ending Account Value (04/30/23)		Expenses Paid During the Period	(a)		Beginning Account Value (11/01/22)		Ending Account Value (04/30/23)		Expenses Paid During the Period	(a)	Annualized Expense Ratio
Institutional	$	1,000.00	$	1,019.20	$	2.10		$	1,000.00	$	1,022.71	$	2.11		0.42	%
Investor A		1,000.00		1,019.20		2.10			1,000.00		1,022.71		2.11		0.42
Investor C		1,000.00		1,015.50		5.85			1,000.00		1,018.99		5.86		1.17

^(a)  For each class of the Fund, expenses are equal to the annualized expense ratio for the class, multiplied by the average account value over the period, multiplied by 181/365 (to reflect the one-half year period shown).

FUND  SUMMARY   /   DISCLOSURE   OF   EXPENSES 5

Schedule of Investments April 30, 2023 BlackRock Summit Cash Reserves Fund (Percentages shown are based on Net Assets)

Security	Par (000)		Value
Short-Term Securities
U.S. Government Sponsored Agency Securities — 38.4%
Federal Farm Credit Banks Funding Corp.
2.25%, 06/07/23	$	640	$	639,995
(1-day SOFR + 0.03%), 4.84%, 07/25/23(a)		1,340		1,339,991
(1-day SOFR + 0.04%), 4.85%, 07/12/23(a)		300		299,997
(1-day SOFR + 0.05%), 4.86%, 08/22/23(a)		2,240		2,240,000
(1-day SOFR + 0.05%), 4.86%, 09/28/23(a)		1,505		1,505,000
(1-day SOFR + 0.05%), 4.86%, 10/16/23(a)		2,445		2,445,000
(1-day SOFR + 0.05%), 4.86%, 02/20/24(a)		6,625		6,625,000
(1-day SOFR + 0.05%), 4.86%, 05/09/24(a)		2,215		2,215,000
(1-day SOFR + 0.06%), 4.87%, 11/22/23(a)		2,780		2,780,000
(1-day SOFR + 0.06%), 4.87%, 01/10/24(a)		425		425,000
(1-day SOFR + 0.09%), 4.90%, 08/26/24(a)		4,280		4,280,000
(1-day SOFR + 0.10%), 4.91%, 08/01/24(a)		1,055		1,055,000
(1-day SOFR + 0.17%), 4.98%, 01/23/25(a)		2,845		2,845,000
Federal Farm Credit Discount Notes(b)
5.13%, 09/11/23		1,420		1,393,769
4.78%, 10/16/23		405		396,212
4.80%, 11/13/23		405		394,747
Federal Home Loan Bank Discount Notes(b)
4.71%, 05/03/23		4,860		4,858,744
4.81%, 05/31/23		3,350		3,336,767
4.93%, 06/16/23		9,160		9,103,023
4.94%, 07/14/23		915		905,859
5.05%, 07/25/23		5,400		5,336,760
4.83%, 08/04/23		1,620		1,599,848
5.12%, 09/01/23		2,675		2,629,393
5.12%, 09/15/23		11,030		10,820,543
4.91%, 02/02/24		1,915		1,846,041
5.02%, 02/09/24		5,180		4,984,668
Federal Home Loan Banks
4.81%, 08/03/23(a)		15,400		15,400,000
3.38%, 09/01/23		3,190		3,187,678
5.40%, 03/27/24		5,070		5,070,000
(1-day SOFR + 0.01%), 4.82%, 08/25/23(a)		8,300		8,300,000
(1-day SOFR + 0.02%), 4.83%, 05/02/23(a)		735		735,000
(1-day SOFR + 0.02%), 4.83%, 05/23/23(a)		15,600		15,600,000
(1-day SOFR + 0.02%), 4.83%, 07/13/23(a)		11,000		11,000,000

Security	Par (000)		Value
U.S. Government Sponsored Agency Securities (continued)
Federal Home Loan Banks (continued)
(1-day SOFR + 0.03%), 4.84%, 05/09/23(a)	$	11,100	$	11,100,000
(1-day SOFR + 0.03%), 4.84%, 05/17/23(a)		9,235		9,235,000
(1-day SOFR + 0.04%), 4.85%, 05/03/23(a)		11,820		11,820,000
(1-day SOFR + 0.04%), 4.85%, 05/26/23(a)		9,600		9,600,000
(1-day SOFR + 0.05%), 4.86%, 05/08/23(a)		12,100		12,100,000
(1-day SOFR + 0.05%), 4.86%, 06/02/23(a)		7,620		7,620,000
(1-day SOFR + 0.07%), 4.95%, 08/22/23(a)		2,315		2,315,000
(1-day SOFR + 0.07%), 4.94%, 09/25/23(a)		1,585		1,585,000
(1-day SOFR + 0.07%), 4.88%, 11/30/23(a)		2,675		2,675,000
(1-day SOFR + 0.08%), 4.89%, 01/24/24(a)		8,800		8,800,000
(1-day SOFR + 0.09%), 4.90%, 05/23/23(a)		3,540		3,540,000
(1-day SOFR + 0.09%), 4.90%, 09/08/23(a)		3,770		3,770,000
(1-day SOFR + 0.10%), 4.91%, 10/06/23(a)		2,220		2,220,000
Freddie Mac, 5.45%, 03/08/24		1,805		1,804,028
				223,778,063
U.S. Treasury Obligations — 1.9%
U.S. Treasury Bills, 2.16%, 05/18/23(b)		835		834,172
U.S. Treasury Floating Rate Notes, (3-mo. Treasury money market yield + 0.20%), 5.33%, 01/31/25(a)		9,000		9,000,000
U.S. Treasury Notes, 1.75%, 05/15/23		1,130		1,129,813
				10,963,985
Total Short-Term Securities —40.3% (Cost: $234,742,048)				234,742,048
Total Repurchase Agreements — 62.1% (Cost: $362,000,000)				362,000,000
Total Investments — 102.4% (Cost: $596,742,048(c))				596,742,048
Liabilities in Excess of Other Assets — (2.4)%				(13,925,473	)
Net Assets — 100.0%			$	582,816,575

^(a)  Variable rate security. Interest rate resets periodically. The rate shown is the effective interest rate as of period end. Security description also includes the reference rate and spread if published and available.

^(b)  Rates are discount rates or a range of discount rates as of period end.

^(c)  Cost for U.S. federal income tax purposes.

6 2 0 2 3   BLACK ROCK  ANNUAL  REPORT   TO  SHAREHOLDERS

Schedule of Investments   (continued) April 30, 2023 BlackRock Summit Cash Reserves Fund

Repurchase Agreements

	Repurchase Agreements												Collateral
Counterparty	Coupon Rate			Purchase Date		Maturity Date		Par (000)		At Value (000)		Proceeds Including Interest	Position	Original Par	Position Received, at Value
BNP Paribas S.A		4.79	%		04/28/23		05/01/23	$	70,000	$	70,000	$ 70,027,942	U.S. Treasury Obligation, 0.25% to 3.00%, due 7/15/25 to 9/30/25	$ 75,343,500	$	71,400,042
BofA Securities, Inc.		4.80			04/28/23		05/01/23		45,000		45,000	45,018,000	U.S. Treasury Obligation, 0.38% to 0.63%, due 1/15/24 to 7/15/27	37,820,900		45,900,050
		4.82			04/28/23		05/01/23		30,000		30,000	30,012,050	U.S. Treasury Obligation, 0.25%, due 11/15/23	31,344,500		30,600,024
Total BofA Securities, Inc.										$	75,000				$	76,500,074
J.P. Morgan Securities LLC		4.79			04/28/23		05/01/23		70,000		70,000	70,027,942	U.S. Treasury Obligation, 4.75%, due 2/15/41	61,884,600		71,400,070
Mizuho Securities USA, Inc.		4.80			04/28/23		05/01/23		67,000		67,000	67,026,800	U.S. Treasury Obligation, 3.50%, due 2/15/33	67,537,800		68,340,036
TD Securities (USA) LLC		4.79			04/28/23		05/01/23		80,000		80,000	80,031,933	U.S. Treasury Obligation, 0.13% to 1.88%, due 2/15/24 to 2/15/32	89,237,500		81,600,077
										$	362,000				$	369,240,299

Fair Value Hierarchy as of Period End

Various inputs are used in determining the fair value of financial instruments. For a description of the input levels and information about the Fund’s policy regarding valuation of financial instruments, refer to the Notes to Financial Statements.

The following table summarizes the Fund’s financial instruments categorized in the fair value hierarchy. The breakdown of the Fund’s financial instruments into major categories is disclosed in the Schedule of Investments above.

	Level 1		Level 2		Level 3		Total
Assets
Investments
Short-Term Securities
Repurchase Agreements	$	—	$	362,000,000	$	—	$	362,000,000
U.S. Government Sponsored Agency Securities		—		223,778,063		—		223,778,063
U.S. Treasury Obligations		—		10,963,985		—		10,963,985
	$	—	$	596,742,048	$	—	$	596,742,048

See notes to financial statements.

SCHEDULE   OF   INVESTMENTS 7

Statement of Assets and Liabilities

April 30, 2023

	BlackRock Summit Cash Reserves Fund
ASSETS
Investments, at value — unaffiliated(a)	$	234,742,048
Cash		898,867
Repurchase agreements, at value(b)		362,000,000
Receivables:
Investments sold		600,000
Capital shares sold		3,532,166
Interest — unaffiliated		1,438,056
Prepaid expenses		70,865
Total assets		603,282,002
LIABILITIES
Payables:
Investments purchased		15,400,000
Accounting services fees		6,665
Capital shares redeemed		4,483,967
Custodian fees		5,228
Income dividend distributions		130,605
Investment advisory fees		341,406
Trustees’ and Officer’s fees		2,005
Other accrued expenses		20,457
Professional fees		53,512
Distribution fees		360
Transfer agent fees		21,222
Total liabilities		20,465,427
NET ASSETS	$	582,816,575
NET ASSETS CONSIST OF
Paid-in capital	$	582,804,388
Accumulated earnings		12,187
NET ASSETS	$	582,816,575
(a)   Investments, at cost — unaffiliated	$	234,742,048
(b)   Repurchase agreements, at cost	$	362,000,000

8 2 0 2 3   BLACK ROCK  ANNUAL  REPORT   TO  SHAREHOLDERS

Statement of Assets and Liabilities  (continued)

April 30, 2023

	BlackRock Summit Cash Reserves Fund
NET ASSET VALUE
Institutional
Net assets	$	97,306,877
Shares outstanding		97,337,491
Net asset value	$	1.00
Shares authorized		Unlimited
Par value	$	0.10
Investor A
Net assets	$	484,689,965
Shares outstanding		484,842,148
Net asset value	$	1.00
Shares authorized		Unlimited
Par value	$	0.10
Investor C
Net assets	$	819,733
Shares outstanding		819,991
Net asset value	$	1.00
Shares authorized		Unlimited
Par value	$	0.10

See notes to financial statements.

FINANCIAL    STATEMENTS 9

Statement of Operations

Year Ended April 30, 2023

	BlackRock Summit Cash Reserves Fund
INVESTMENT INCOME
Interest — unaffiliated	$	16,775,215
Total investment income		16,775,215
EXPENSES
Investment advisory		2,674,166
Transfer agent — class specific		154,133
Registration		104,057
Professional		101,405
Printing and postage		30,334
Accounting services		26,477
Custodian		21,542
Trustees and Officer		11,324
Distribution — class specific		7,652
Miscellaneous		20,700
Total expenses		3,151,790
Less:
Fees waived and/or reimbursed by the Manager		(775,719	)
Distribution fees waived and/or reimbursed — class specific		(593	)
Transfer agent fees waived and/or reimbursed by the Manager — class specific		(152,729	)
Total expenses after fees waived and/or reimbursed		2,222,749
Net investment income		14,552,466
REALIZED AND UNREALIZED GAIN (LOSS)
Net realized gain from:
Investments — unaffiliated		7,043
Net realized and unrealized gain		7,043
NET INCREASE IN NET ASSETS RESULTING FROM OPERATIONS	$	14,559,509

See notes to financial statements.

10 2 0 2 3   BLACK ROCK  ANNUAL  REPORT   TO  SHAREHOLDERS

Statements of Changes in Net Assets

	BlackRock Summit Cash Reserves Fund
	Year Ended 04/30/23			Year Ended 04/30/22
INCREASE (DECREASE) IN NET ASSETS
OPERATIONS
Net investment income	$	14,552,466		$	47,076
Net realized gain		7,043			9,033
Net increase in net assets resulting from operations		14,559,509			56,109
DISTRIBUTIONS TO SHAREHOLDERS(a)
Institutional		(2,608,344	)		(8,045	)
Investor A		(11,926,437	)		(62,604	)
Investor C		(17,812	)		(194	)
Decrease in net assets resulting from distributions to shareholders		(14,552,593	)		(70,843	)
CAPITAL SHARE TRANSACTIONS
Net increase in net assets derived from capital share transactions		123,541,067			24,251,766
NET ASSETS
Total increase in net assets		123,547,983			24,237,032
Beginning of year		459,268,592			435,031,560
End of year	$	582,816,575		$	459,268,592

^(a)  Distributions for annual periods determined in accordance with U.S. federal income tax regulations.

See notes to financial statements.

FINANCIAL    STATEMENTS 11

Financial Highlights

(For a share outstanding throughout each period)

	BlackRock Summit Cash Reserves Fund
	Institutional
			Year Ended 04/30/23			Year Ended 04/30/22			Year Ended 04/30/21			Period from 07/15/19 to 04/30/20	(a)
Net asset value, beginning of period		$	1.00		$	1.00		$	1.00		$	1.00
Net investment income			0.0263			0.0001			0.0000	(b)		0.0098
Net realized and unrealized gain			0.0000	(b)		0.0000	(b)		0.0003			0.0000	(b)
Net increase from investment operations			0.0263			0.0001			0.0003			0.0098
Distributions(c)
From net investment income			(0.0263	)		(0.0001	)		(0.0000	)(d)		(0.0098	)
From net realized gain			(0.0000	)(d)		(0.0000	)(d)		(0.0003	)		(0.0000	)(d)
Total distributions			(0.0263	)		(0.0001	)		(0.0003	)		(0.0098	)
Net asset value, end of period		$	1.00		$	1.00		$	1.00		$	1.00
Total Return(e)
Based on net asset value			2.66	%		0.01	%		0.03	%		0.98	%(f)
Ratios to Average Net Assets
Total expenses			0.59	%		0.60	%		0.61	%		0.64	%(g)(h)
Total expenses after fees waived and/or reimbursed			0.41	%		0.12	%		0.17	%		0.42	%(g)(h)
Net investment income			2.66	%		0.00	%(i)		0.00	%(i)		1.20	%(h)
Supplemental Data
Net assets, end of period (000)		$	97,307		$	101,901		$	87,699		$	97,718

^(a)  Commencement of operations.

^(b)  Amount is less than $0.00005 per share.

^(c)  Distributions for annual periods determined in accordance with U.S. federal income tax regulations.

^(d)  Amount is greater than $(0.00005) per share.

^(e)  Where applicable, assumes the reinvestment of distributions.

^(f)  Not annualized.

^(g)  Includes non-recurring expenses of offering, organization and reorganization costs. Without these costs, total expenses and total expenses after fees waived and/or reimbursed would have been 0.62% and 0.39% for the period ended 04/30/2020, respectively.

^(h)  Annualized.

⁽ⁱ⁾  Amount is less than 0.005%.

See notes to financial statements.

12 2 0 2 3   BLACK ROCK  ANNUAL  REPORT   TO  SHAREHOLDERS

Financial Highlights (continued)

(For a share outstanding throughout each period)

	BlackRock Summit Cash Reserves Fund (continued)
	Investor A
			Year Ended 04/30/23			Year Ended 04/30/22			Year Ended 04/30/21			Year Ended 04/30/20			Year Ended 04/30/19
Net asset value, beginning of year		$	1.00		$	1.00		$	1.00		$	1.00		$	1.00
Net investment income			0.0263			0.0002			0.0000	(a)		0.0142			0.0135
Net realized and unrealized gain			0.0000	(a)		0.0000	(a)		0.0003			0.0000	(a)		0.0000	(a)
Net increase from investment operations			0.0263			0.0002			0.0003			0.0142			0.0135
Distributions(b)
From net investment income			(0.0263	)		(0.0002	)		(0.0000	)(c)		(0.0142	)		(0.0135	)
From net realized gain			(0.0000	)(c)		(0.0000	)(c)		(0.0003	)		(0.0000	)(c)		(0.0000	)(c)
Total distributions			(0.0263	)		(0.0002	)		(0.0003	)		(0.0142	)		(0.0135	)
Net asset value, end of year		$	1.00		$	1.00		$	1.00		$	1.00		$	1.00
Total Return(d)
Based on net asset value			2.66	%		0.02	%		0.04	%		1.43	%		1.35	%
Ratios to Average Net Assets
Total expenses			0.59	%		0.61	%		0.60	%		0.64	%(e)		0.82	%(e)
Total expenses after fees waived and/or reimbursed			0.41	%		0.10	%		0.17	%		0.42	%(e)		0.52	%(e)
Net investment income			2.74	%		0.01	%		0.00	%(f)		1.36	%		1.86	%
Supplemental Data
Net assets, end of year (000)		$	484,690		$	356,419		$	346,281		$	405,760		$	319,960

^(a)  Amount is less than $0.00005 per share.

^(b)  Distributions for annual periods determined in accordance with U.S. federal income tax regulations.

^(c)  Amount is greater than $(0.00005) per share.

^(d)  Where applicable, assumes the reinvestment of distributions.

^(e)  Includes non-recurring expenses of offering, organization and reorganization costs. Without these costs, total expenses and total expenses after fees waived and/or reimbursed would have been 0.61% and 0.40% for the year ended 04/30/20, respectively, and 0.72% and 0.42% for the year ended 04/30/19, respectively.

^(f)  Amount is less than 0.005%.

See notes to financial statements.

FINANCIAL    HIGHLIGHTS 13

Financial Highlights (continued)

(For a share outstanding throughout each period)

	BlackRock Summit Cash Reserves Fund (continued)
	Investor C
			Year Ended 04/30/23			Year Ended 04/30/22			Year Ended 04/30/21			Year Ended 04/30/20			Period from 08/10/18 to 04/30/19	(a)
Net asset value, beginning of period		$	1.00		$	1.00		$	1.00		$	1.00		$	1.00
Net investment income			0.0194			0.0002			0.0000	(b)		0.0075			0.0058
Net realized and unrealized gain			0.0000	(b)		0.0000	(b)		0.0003			0.0000	(b)		0.0000	(b)
Net increase from investment operations			0.0194			0.0002			0.0003			0.0075			0.0058
Distributions(c)
From net investment income			(0.0194	)		(0.0002	)		(0.0000	)(d)		(0.0075	)		(0.0058	)
From net realized gain			(0.0000	)(d)		(0.0000	)(d)		(0.0003	)		(0.0000	)(d)		(0.0000	)(d)
Total distributions			(0.0194	)		(0.0002	)		(0.0003	)		(0.0075	)		(0.0058	)
Net asset value, end of period		$	1.00		$	1.00		$	1.00		$	1.00		$	1.00
Total Return(e)
Based on net asset value			1.96	%		0.03	%		0.04	%		0.75	%		0.58	%(f)
Ratios to Average Net Assets
Total expenses			1.35	%		1.46	%		1.38	%		1.52	%(g)		1.47	%(g)(h)
Total expenses after fees waived and/or reimbursed			1.11	%		0.10	%		0.20	%		0.90	%(g)		1.20	%(g)(h)
Net investment income			1.75	%		0.02	%		0.00	%(i)		0.51	%		1.25	%(h)
Supplemental Data
Net assets, end of period (000)		$	820		$	948		$	1,052		$	1,956		$	651

^(a)  Commencement of operations.

^(b)  Amount is less than $0.00005 per share.

^(c)  Distributions for annual periods determined in accordance with U.S. federal income tax regulations.

^(d)  Amount is greater than $(0.00005) per share.

^(e)  Where applicable, excludes the effects of any sales charges and assumes the reinvestment of distributions.

^(f)  Not annualized.

^(g)  Includes non-recurring expenses of offering, organization and reorganization costs. Without these costs, total expenses and total expenses after fees waived and/or reimbursed would have been 1.49% and 0.87% for the year ended 04/30/20, respectively, and 1.38% and 1.11% for the period ended 04/30/19, respectively.

^(h)  Annualized.

⁽ⁱ⁾  Amount is less than 0.005%.

See notes to financial statements.

14 2 0 2 3   BLACK ROCK  ANNUAL  REPORT   TO  SHAREHOLDERS

Notes to Financial Statements

1. ORGANIZATION

BlackRock Financial Institutions Series Trust (the “Trust”) is registered under the Investment Company Act of 1940, as amended (the “1940 Act”), as an open-end management investment company. The Trust is organized as a Massachusetts business trust. BlackRock Summit Cash Reserves Fund (the “Fund”) is a series of the Trust. The Fund is classified as diversified.

The Fund offers multiple classes of shares. All classes of shares have identical voting, dividend, liquidation and other rights and are subject to the same terms and conditions, except that certain classes bear expenses related to the shareholder servicing and distribution of such shares. Institutional Shares are sold without a sales charge and only to certain eligible investors. Investor A and Investor C Shares may be subject to a contingent deferred sales charge (“CDSC”). Investor A Shares are generally available through financial intermediaries. Investor C Shares are available only through exchanges and dividend and capital gain reinvestments by current holders. Investor C Shares automatically convert to Investor A Shares after approximately eight years. Each class has exclusive voting rights with respect to matters relating to its shareholder servicing and distribution expenditures.

The Fund operates as a “government money market fund” under Rule 2a-7 under the 1940 Act. The Fund is not subject to liquidity fees or temporary suspensions of redemptions due to declines in the Fund’s weekly liquid assets.

The Fund, together with certain other registered investment companies advised by BlackRock Advisors, LLC (the “Manager”) or its affiliates, is included in a complex of funds referred to as the BlackRock Multi-Asset Complex.

2. SIGNIFICANT ACCOUNTING POLICIES

The financial statements are prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”), which may require management to make estimates and assumptions that affect the reported amounts of assets and liabilities in the financial statements, disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of increases and decreases in net assets from operations during the reporting period. Actual results could differ from those estimates. The Fund is considered an investment company under U.S. GAAP and follows the accounting and reporting guidance applicable to investment companies. Below is a summary of significant accounting policies:

Investment Transactions and Income Recognition: For financial reporting purposes, investment transactions are recorded on the dates the transactions are executed. Realized gains and losses on investment transactions are determined using the specific identification method. Interest income, including amortization and accretion of premiums and discounts on debt securities, is recognized daily on an accrual basis. Income, expenses and realized and unrealized gains and losses are allocated daily to each class based on its relative net assets.

Distributions: Distributions from net investment income are declared daily and paid monthly. Distributions of capital gains are distributed at least annually and are recorded on the ex-dividend dates. The character and timing of distributions are determined in accordance with U.S. federal income tax regulations, which may differ from U.S. GAAP.

Offering Costs: Offering costs are amortized over a 12-month period beginning with the commencement of operations of a class of shares.

Indemnifications: In the normal course of business, the Fund enters into contracts that contain a variety of representations that provide general indemnification. The Fund’s maximum exposure under these arrangements is unknown because it involves future potential claims against the Fund, which cannot be predicted with any certainty.

Other: Expenses directly related to the Fund or its classes are charged to the Fund or the applicable class. Expenses directly related to the Fund and other shared expenses prorated to the Fund are allocated daily to each class based on its relative net assets or other appropriate methods. Other operating expenses shared by several funds, including other funds managed by the Manager, are prorated among those funds on the basis of relative net assets or other appropriate methods.

3. INVESTMENT VALUATION AND FAIR VALUE MEASUREMENTS

Investment Valuation Policies: U.S. GAAP defines fair value as the price the Fund would receive to sell an asset or pay to transfer a liability in an orderly transaction between market participants at the measurement date. The Fund’s investments are valued under the amortized cost method which approximates current market value in accordance with Rule 2a-7 under the 1940 Act. Under this method, investments are valued at cost when purchased and, thereafter, a constant proportionate accretion of discounts and amortization of premiums are recorded until the maturity of the security. The Fund seeks to maintain its net asset value (“NAV”) per share at $1.00, although there is no assurance that it will be able to do so on a continuing basis.

Fair Value Hierarchy: Various inputs are used in determining the fair value of financial instruments. These inputs to valuation techniques are categorized into a fair value hierarchy consisting of three broad levels for financial reporting purposes as follows:

• Level 1 – Unadjusted price quotations in active markets/exchanges for identical assets or liabilities that the Fund has the ability to access;

• Level 2 – Other observable inputs (including, but not limited to, quoted prices for similar assets or liabilities in markets that are active, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the assets or liabilities (such as interest rates, yield curves, volatilities, prepayment speeds, loss severities, credit risks and default rates) or other market–corroborated inputs); and

• Level 3 – Unobservable inputs based on the best information available in the circumstances, to the extent observable inputs are not available (including the Valuation Committee’s assumptions used in determining the fair value of financial instruments).

NOTES   TO   FINANCIAL   STATEMENTS 15

Notes to Financial Statements  (continued)

The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements) and the lowest priority to unobservable inputs (Level 3 measurements). Accordingly, the degree of judgment exercised in determining fair value is greatest for instruments categorized in Level 3. The inputs used to measure fair value may fall into different levels of the fair value hierarchy. In such cases, for disclosure purposes, the fair value hierarchy classification is determined based on the lowest level input that is significant to the fair value measurement in its entirety. The categorization of a value determined for financial instruments is based on the pricing transparency of the financial instruments and is not necessarily an indication of the risks associated with investing in those securities.

4. SECURITIES AND OTHER INVESTMENTS

Repurchase Agreements: Repurchase agreements are commitments to purchase a security from a counterparty who agrees to repurchase the same security at a mutually agreed upon date and price. On a daily basis, the counterparty is required to maintain eligible collateral subject to the agreement and in value no less than the agreed upon repurchase amount. Repurchase agreements may be traded bilaterally, in a tri-party arrangement or may be centrally cleared through a sponsoring agent. Subject to the custodial undertaking associated with a tri-party repurchase arrangement and for centrally cleared repurchase agreements, a third-party custodian maintains accounts to hold collateral for the fund and its counterparties. Typically, the fund and counterparty are not permitted to sell, re-pledge or use the collateral absent a default by the counterparty or the fund, respectively.

In the event the counterparty defaults and the fair value of the collateral declines, a fund could experience losses, delays and costs in liquidating the collateral.

Repurchase agreements are entered into by a fund under Master Repurchase Agreements (each, an “MRA”). The MRA permits a fund, under certain circumstances including an event of default (such as bankruptcy or insolvency), to offset payables and/or receivables with collateral held by and/or posted to the counterparty. As a result, one single net payment is created. Bankruptcy or insolvency laws of a particular jurisdiction may impose restrictions on or prohibitions against such a right of offset in the event of the MRA counterparty’s bankruptcy or insolvency. Based on the terms of the MRA, the fund receives collateral with a market value in excess of the repurchase price at maturity. Upon a bankruptcy or insolvency of the MRA counterparty, the fund would recognize a liability with respect to such excess collateral. The liability reflects a fund’s obligation under bankruptcy law to return the excess to the counterparty.

5. INVESTMENT ADVISORY AGREEMENT AND OTHER TRANSACTIONS WITH AFFILIATES

Investment Advisory: The Trust, on behalf of the Fund, entered into an Investment Advisory Agreement with the Manager, the Fund’s investment adviser and an indirect, wholly-owned subsidiary of BlackRock, Inc. (“BlackRock”), to provide investment advisory and administrative services. The Manager is responsible for the management of the Fund’s portfolio and provides the personnel, facilities, equipment and certain other services necessary to the operations of the Fund.

For such services, the Fund pays the Manager a monthly fee at an annual rate equal to 0.50% of the average daily value of the Fund’s net assets.

Distribution Fees: The Trust, on behalf of the Fund, entered into a Distribution Agreement and a Distribution Plan with BlackRock Investments, LLC (“BRIL”), an affiliate of the Manager. Pursuant to the Distribution Plan and in accordance with Rule 12b-1 under the 1940 Act, the Fund pays BRIL ongoing distribution fees. The fees are accrued daily and paid monthly at annual rates based upon the average daily net assets of the relevant share class of the Fund as follows:

Share Class	Distribution Fees
Investor C	0.75%

BRIL and broker-dealers, pursuant to sub-agreements with BRIL, provide shareholder distribution services to the Fund. The ongoing distribution fee compensates BRIL and each broker-dealer for providing shareholder distribution related services to shareholders.

For the year ended April 30, 2023, the following table shows the class specific distribution fees borne directly by each share class of the Fund:

	Investor C
Distribution fees — class specific	$    7,652

Transfer Agent: Pursuant to written agreements, certain financial intermediaries, some of which may be affiliates, provide the Fund with sub-accounting, recordkeeping, sub-transfer agency and other administrative services with respect to servicing of underlying investor accounts. For these services, these entities receive an asset-based fee or an annual fee per shareholder account, which will vary depending on share class and/or net assets. For the year ended April 30, 2023, the Fund did not pay any amounts to affiliates in return for these services.

The Manager maintains a call center that is responsible for providing certain shareholder services to the Fund. Shareholder services include responding to inquiries and processing purchases and sales based upon instructions from shareholders. For the year ended April 30, 2023, the Fund reimbursed the Manager the following amounts for costs incurred in running the call center, which are included in transfer agent — class specific in the Statement of Operations:

Fund Name	Investor A		Investor C		Total
BlackRock Summit Cash Reserves Fund	$	11,746	$	149	$11,895

For the year ended April 30, 2023, the following table shows the class specific transfer agent fees borne directly by each share class of the Fund:

	Institutional		Investor A		Investor C		Total
Transfer agent fees — class specific	$	28,791	$	124,924	$	418	$ 154,133

16     2 0 2 3   BLACK ROCK  ANNUAL  REPORT   TO  SHAREHOLDERS

Notes to Financial Statements  (continued)

Other Fees: For the year ended April 30, 2023, affiliates received CDSCs as follows:

	Investor A		Investor C		Total
CDSC	$	70,278	$	216	$70,494

Expense Limitations, Waivers and Reimbursements: With respect to the Fund, the Manager contractually agreed to waive and/or reimburse fees or expenses in order to limit expenses, excluding interest expense, dividend expense, tax expense, acquired fund fees and expenses, and certain other fund expenses, which constitute extraordinary expenses not incurred in the ordinary course of the Fund’s business (“expense limitation”). The expense limitation as a percentage of average daily net assets is as follows:

Share Class	Expense Limitation
Institutional		0.42	%
Investor A		0.42
Investor C		1.17

The Manager has agreed not to reduce or discontinue the contractual expense limitations through June 30, 2024, unless approved by the Board, including a majority of the trustees who are not “interested persons” of the Trust, as defined in the 1940 Act (“Independent Trustees”), or by a vote of a majority of the outstanding voting securities of the Fund. For the year ended April 30, 2023, the Manager waived and/or reimbursed $750,601 which is included in fees waived and/or reimbursed by the Manager in the Statement of Operations.

In addition, these amounts waived and/or reimbursed are included in distribution fees waived and/or reimbursed — class specific and transfer agent fees waived and/or reimbursed by the Manager—class specific in the Statement of Operations. For the year ended April 30, 2023, class specific expense waivers and/or reimbursements are as follows:

	Investor C
Distribution fees waived and/or reimbursed — class specific	$         558

	Institutional		Investor A		Investor C		Total
Transfer agent fees waived and/or reimbursed by the Manager — class specific	$	28,300	$	124,015	$	414	$	152,729

The Manager and BRIL have also voluntarily agreed to waive a portion of their respective management, investment advisory and service and distribution fees and/or reimburse operating expenses to enable the Fund to maintain minimum levels of daily net investment income if applicable. These amounts, if any, are reported in the Statement of Operations as fees waived and/or reimbursed by the Manager and Distribution fees waived and/or reimbursed — class specific. The Manager and BRIL may discontinue the waiver and/or reimbursement at any time. For the year ended April 30, 2023, the amounts waived and/or reimbursed were as follows:

	Investor C
Distribution fees waived and/or reimbursed — class specific	$	35
Fees waived and/or reimbursed by the Manager	$	25,118

Trustees and Officers: Certain trustees and/or officers of the Trust are directors and/or officers of BlackRock or its affiliates. The Fund reimburses the Manager for a portion of the compensation paid to the Trust’s Chief Compliance Officer, which is included in Trustees and Officer in the Statement of Operations.

6. INCOME TAX INFORMATION

It is the Fund’s policy to comply with the requirements of the Internal Revenue Code of 1986, as amended, applicable to regulated investment companies, and to distribute substantially all of its taxable income to its shareholders. Therefore, no U.S. federal income tax provision is required.

The Fund files U.S. federal and various state and local tax returns. No income tax returns are currently under examination. The statute of limitations on the Fund’s U.S. federal tax returns generally remains open for a period of three years after they are filed. The statutes of limitations on the Fund’s state and local tax returns may remain open for an additional year depending upon the jurisdiction.

Management has analyzed tax laws and regulations and their application to the Fund as of April 30, 2023, inclusive of the open tax return years, and does not believe that there are any uncertain tax positions that require recognition of a tax liability in the Fund’s financial statements.

The tax character of distributions paid was as follows:

Fund Name	Year Ended 04/30/23		Year Ended 04/30/22
BlackRock Summit Cash Reserves Fund Ordinary income	$	14,552,593	$	70,843

As of April 30, 2023, the tax components of accumulated earnings (loss) were as follows:

Fund Name	Undistributed Ordinary Income
BlackRock Summit Cash Reserves Fund	$	12,187

NOTES   TO   FINANCIAL   STATEMENTS 17

Notes to Financial Statements  (continued)

7. PRINCIPAL RISKS

In the normal course of business, the Fund invests in securities or other instruments and may enter into certain transactions, and such activities subject the Fund to various risks, including among others, fluctuations in the market (market risk) or failure of an issuer to meet all of its obligations. The value of securities or other instruments may also be affected by various factors, including, without limitation: (i) the general economy; (ii) the overall market as well as local, regional or global political and/or social instability; (iii) regulation, taxation or international tax treaties between various countries; or (iv) currency, interest rate and price fluctuations. Local, regional or global events such as war, acts of terrorism, the spread of infectious illness or other public health issues, recessions, or other events could have a significant impact on the Fund and its investments. The Fund’s prospectus provides details of the risks to which the Fund is subject.

Infectious Illness Risk: An outbreak of an infectious illness, such as the COVID-19 pandemic, may adversely impact the economies of many nations and the global economy, and may impact individual issuers and capital markets in ways that cannot be foreseen. An infectious illness outbreak may result in, among other things, closed international borders, prolonged quarantines, supply chain disruptions, market volatility or disruptions and other significant economic, social and political impacts.

Counterparty Credit Risk: The Fund may be exposed to counterparty credit risk, or the risk that an entity may fail to or be unable to perform on its commitments related to unsettled or open transactions, including making timely interest and/or principal payments or otherwise honoring its obligations. The Fund manages counterparty credit risk by entering into transactions only with counterparties that the Manager believes have the financial resources to honor their obligations and by monitoring the financial stability of those counterparties. Financial assets, which potentially expose the Fund to market, issuer and counterparty credit risks, consist principally of financial instruments and receivables due from counterparties. The extent of the Fund’s exposure to market, issuer and counterparty credit risks with respect to these financial assets is approximately their value recorded in the Statement of Assets and Liabilities, less any collateral held by the Fund.

Concentration Risk: A diversified portfolio, where this is appropriate and consistent with a fund’s objectives, minimizes the risk that a price change of a particular investment will have a material impact on the NAV of a fund. The investment concentrations within the Fund’s portfolio are disclosed in its Schedule of Investments.

The Fund invests a significant portion of its assets in securities of issuers located in the United States. A decrease in imports or exports, changes in trade regulations, inflation and/or an economic recession in the United States may have a material adverse effect on the U.S. economy and the securities listed on U.S. exchanges. Proposed and adopted policy and legislative changes in the United States may also have a significant effect on U.S. markets generally, as well as on the value of certain securities. Governmental agencies project that the United States will continue to maintain elevated public debt levels for the foreseeable future which may constrain future economic growth. Circumstances could arise that could prevent the timely payment of interest or principal on U.S. government debt, such as reaching the legislative “debt ceiling.” Such non-payment would result in substantial negative consequences for the U.S. economy and the global financial system. If U.S. relations with certain countries deteriorate, it could adversely affect issuers that rely on the United States for trade. The United States has also experienced increased internal unrest and discord. If these trends were to continue, they may have an adverse impact on the U.S. economy and the issuers in which the Fund invests.

Significant Shareholder Redemption Risk: Certain shareholders may own or manage a substantial amount of fund shares and/or hold their fund investments for a limited period of time. Large redemptions of fund shares by these shareholders may force a fund to sell portfolio securities, which may negatively impact the fund’s NAV, increase the fund’s brokerage costs, and/or accelerate the realization of taxable income/gains and cause the fund to make additional taxable distributions to shareholders.

8. CAPITAL SHARE TRANSACTIONS

The number of shares sold, reinvested and redeemed corresponds to the net proceeds from the sale of shares, reinvestment of all distributions and cost of shares redeemed, respectively, since shares are sold and redeemed at $1.00 per share.

Transactions in capital shares for each class were as follows:

Share Class	Year Ended 04/30/23			Year Ended 04/30/22
Institutional
Shares sold		85,998,626			70,750,432
Shares issued in reinvestment of distributions		2,556,959			7,891
Shares redeemed		(93,161,642	)		(56,549,307	)
		(4,606,057	)		14,209,016
Investor A
Shares sold		422,593,014			146,511,218
Shares issued in reinvestment of distributions		11,698,275			61,245
Shares redeemed		(306,015,734	)		(136,426,020	)
		128,275,555			10,146,443
Investor C
Shares sold		1,507,820			752,536
Shares issued in reinvestment of distributions		16,640			178
Shares redeemed		(1,652,891	)		(856,407	)
		(128,431	)		(103,693	)
		123,541,067			24,251,766

18     2 0 2 3   BLACK ROCK  ANNUAL  REPORT   TO  SHAREHOLDERS

Notes to Financial Statements  (continued)

As of April 30, 2023, BlackRock Financial Management, Inc., an affiliate of the Fund, owned 50,000 Investor C Shares of the Fund.

9. SUBSEQUENT EVENTS

Management has evaluated the impact of all subsequent events on the Fund through the date the financial statements were issued and has determined that there were no subsequent events requiring adjustment or additional disclosure in the financial statements.

NOTES   TO   FINANCIAL   STATEMENTS 19

Report of Independent Registered Public Accounting Firm

To the Shareholders of BlackRock Summit Cash Reserves Fund and the Board of Trustees of BlackRock Financial Institutions Series Trust:

Opinion on the Financial Statements and Financial Highlights

We have audited the accompanying statement of assets and liabilities of BlackRock Summit Cash Reserves Fund of BlackRock Financial Institutions Series Trust (the “Fund”), including the schedule of investments, as of April 30, 2023, the related statement of operations for the year then ended, the statements of changes in net assets for each of the two years in the period then ended, the financial highlights for each of the five years in the period then ended, and the related notes. In our opinion, the financial statements and financial highlights present fairly, in all material respects, the financial position of the Fund as of April 30, 2023, and the results of its operations for the year then ended, the changes in its net assets for each of the two years in the period then ended, and the financial highlights for each of the five years in the period then ended, in conformity with accounting principles generally accepted in the United States of America.

Basis for Opinion

These financial statements and financial highlights are the responsibility of the Fund’s management. Our responsibility is to express an opinion on the Fund’s financial statements and financial highlights based on our audits. We are a public accounting firm registered with the Public Company Accounting Oversight Board (United States) (PCAOB) and are required to be independent with respect to the Fund in accordance with the U.S. federal securities laws and the applicable rules and regulations of the Securities and Exchange Commission and the PCAOB.

We conducted our audits in accordance with the standards of the PCAOB. Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements and financial highlights are free of material misstatement, whether due to error or fraud. The Fund is not required to have, nor were we engaged to perform, an audit of its internal control over financial reporting. As part of our audits we are required to obtain an understanding of internal control over financial reporting but not for the purpose of expressing an opinion on the effectiveness of the Fund’s internal control over financial reporting. Accordingly, we express no such opinion.

Our audits included performing procedures to assess the risks of material misstatement of the financial statements and financial highlights, whether due to error or fraud, and performing procedures that respond to those risks. Such procedures included examining, on a test basis, evidence regarding the amounts and disclosures in the financial statements and financial highlights. Our audits also included evaluating the accounting principles used and significant estimates made by management, as well as evaluating the overall presentation of the financial statements and financial highlights. Our procedures included confirmation of securities owned as of April 30, 2023, by correspondence with custodians or counterparties; when replies were not received, we performed other auditing procedures. We believe that our audits provide a reasonable basis for our opinion.

Deloitte & Touche LLP

Boston, Massachusetts

June 22, 2023

We have served as the auditor of one or more BlackRock investment companies since 1992.

20     2 0 2 3   BLACK ROCK  ANNUAL  REPORT   TO  SHAREHOLDERS

Important Tax Information  (unaudited)

The Fund hereby designates the following amount, or maximum amount allowable by law, of distributions from direct federal obligation interest for the fiscal year ended April 30, 2023:

Fund Name	Federal Obligation Interest
BlackRock Summit Cash Reserves Fund	$	6,649,854

The law varies in each state as to whether and what percent of ordinary income dividends attributable to federal obligations is exempt from state income tax. Shareholders are advised to check with their tax advisers to determine if any portion of the dividends received is exempt from state income tax.

The Fund hereby designates the following amount, or maximum amount allowable by law, as interest income eligible to be treated as a Section 163(j) interest dividend for the fiscal year ended April 30, 2023:

Fund Name	Interest Dividends
BlackRock Summit Cash Reserves Fund	$	14,552,413

The Fund hereby designates the following amount, or maximum amount allowable by law, as interest-related dividends and qualified short-term capital gains eligible for exemption from U.S. withholding tax for nonresident aliens and foreign corporations for the fiscal year ended April 30, 2023:

Fund Name	Interest Related Dividends		Qualified Short-Term Capital Gains
BlackRock Summit Cash Reserves Fund	$	14,552,413	$	7,043

IMPORTANT   TAX   INFORMATION 21

Trustee and Officer Information

Independent Trustees(a)
Name Year of Birth(b)	Position(s) Held (Length of Service)(c)	Principal Occupation(s) During Past 5 Years	Number of BlackRock-Advised Registered Investment Companies (“RICs”) Consisting of Investment Portfolios (“Portfolios”) Overseen	Public Company and Other Investment Company Directorships Held During Past 5 Years
Mark Stalnecker 1951	Chair of the Board (Since 2019) and Trustee (Since 2015)	Chief Investment Officer, University of Delaware from 1999 to 2013; Trustee and Chair of the Finance and Investment Committees, Winterthur Museum and Country Estate from 2005 to 2016; Member of the Investment Committee, Delaware Public Employees’ Retirement System since 2002; Member of the Investment Committee, Christiana Care Health System from 2009 to 2017; Member of the Investment Committee, Delaware Community Foundation from 2013 to 2014; Director and Chair of the Audit Committee, SEI Private Trust Co. from 2001 to 2014.	28 RICs consisting of 166 Portfolios	None
Susan J. Carter 1956	Trustee (Since 2016)	Trustee, Financial Accounting Foundation from 2017 to 2021; Advisory Board Member, Center for Private Equity and Entrepreneurship at Tuck School of Business from 1997 to 2021; Director, Pacific Pension Institute from 2014 to 2018; Senior Advisor, Commonfund Capital, Inc. (“CCI”) (investment adviser) in 2015; Chief Executive Officer, CCI from 2013 to 2014; President & Chief Executive Officer, CCI from 1997 to 2013; Advisory Board Member, Girls Who Invest from 2015 to 2018 and Board Member thereof from 2018 to 2022; Advisory Board Member, Bridges Fund Management since 2016; Practitioner Advisory Board Member, Private Capital Research Institute (“PCRI”) since 2017; Lecturer in the Practice of Management, Yale School of Management since 2019; Advisor to Finance Committee, Altman Foundation since 2020; Investment Committee Member, Tostan since 2021; Member of the President’s Counsel, Commonfund since 2023.	28 RICs consisting of 166 Portfolios	None
Collette Chilton 1958	Trustee (Since 2015)	Chief Investment Officer, Williams College since 2006; Chief Investment Officer, Lucent Asset Management Corporation from 1998 to 2006; Director, Boys and Girls Club of Boston since 2017; Director, B1 Capital since 2018; Director, David and Lucile Packard Foundation since 2020.	28 RICs consisting of 166 Portfolios	None
Neil A. Cotty 1954	Trustee (Since 2016)	Bank of America Corporation from 1996 to 2015, serving in various senior finance leadership roles, including Chief Accounting Officer from 2009 to 2015, Chief Financial Officer of Global Banking, Markets and Wealth Management from 2008 to 2009, Chief Accounting Officer from 2004 to 2008, Chief Financial Officer of Consumer Bank from 2003 to 2004, Chief Financial Officer of Global Corporate Investment Bank from 1999 to 2002.	28 RICs consisting of 166 Portfolios	None
Lena G. Goldberg 1949	Trustee (Since 2019)	Director, Pioneer Legal Institute since 2023; Director, Charles Stark Draper Laboratory, Inc. from 2013 to 2021; Senior Lecturer, Harvard Business School from 2008 to 2021; FMR LLC/Fidelity Investments (financial services) from 1996 to 2008, serving in various senior roles including Executive Vice President - Strategic Corporate Initiatives and Executive Vice President and General Counsel; Partner, Sullivan & Worcester LLP from 1985 to 1996 and Associate thereof from 1979 to 1985.	28 RICs consisting of 166 Portfolios	None

22 2 0 2 3   BLACK ROCK  ANNUAL  REPORT   TO  SHAREHOLDERS

Trustee and Officer Information  (continued)

Independent Trustees(a) (continued)
Name Year of Birth(b)	Position(s) Held (Length of Service)(c)	Principal Occupation(s) During Past 5 Years	Number of BlackRock-Advised Registered Investment Companies (“RICs”) Consisting of Investment Portfolios (“Portfolios”) Overseen	Public Company and Other Investment Company Directorships Held During Past 5 Years
Henry R. Keizer 1956	Trustee (Since 2019)	Director, Park Indemnity Ltd. (captive insurer) from 2010 to 2022.	28 RICs consisting of 166 Portfolios	GrafTech International Ltd. (materials manufacturing); Sealed Air Corp. (packaging); WABCO (commercial vehicle safety systems) from 2015 to 2020; Hertz Global Holdings (car rental) from 2015 to 2021
Cynthia A. Montgomery 1952	Trustee (Since 2007)	Professor, Harvard Business School since 1989.	28 RICs consisting of 166 Portfolios	None
Donald C. Opatrny 1952	Trustee (Since 2019)	Chair of the Board of Phoenix Art Museum since 2022 and Trustee thereof since 2018; Chair of the Investment Committee of The Arizona Community Foundation since 2022 and trustee thereof since 2020; Director, Athena Capital Advisors LLC (investment management firm) from 2013 to 2020; Trustee, Vice Chair, Member of the Executive Committee and Chair of the Investment Committee, Cornell University from 2004 to 2019; President and Trustee, the Center for the Arts, Jackson Hole from 2011 to 2018; Member of the Board and Investment Committee, University School from 2007 to 2018; Member of Affordable Housing Supply Board of Jackson, Wyoming since 2017; Member, Investment Funds Committee, State of Wyoming since 2017; Trustee, Artstor (a Mellon Foundation affiliate) from 2010 to 2015; Member of the Investment Committee, Mellon Foundation from 2009 to 2015; President, Trustee and Member of the Investment Committee, The Aldrich Contemporary Art Museum from 2007 to 2014; Trustee and Chair of the Investment Committee, Community Foundation of Jackson Hole since 2014.	28 RICs consisting of 166 Portfolios	None
Kenneth L. Urish 1951	Trustee (Since 2007)	Managing Partner, Urish Popeck & Co., LLC (certified public accountants and consultants) since 1976; Past- Chairman of the Professional Ethics Committee of the Pennsylvania Institute of Certified Public Accountants and Committee Member thereof since 2007; Member of External Advisory Board, The Pennsylvania State University Accounting Department since 2001, Emeritus since 2022; Principal, UP Strategic Wealth Investment Advisors, LLC since 2013; Trustee, The Holy Family Institute from 2001 to 2010; President and Trustee, Pittsburgh Catholic Publishing Associates from 2003 to 2008; Director, Inter-Tel from 2006 to 2007; Member, Advisory Board, ESG Competent Boards since 2020.	28 RICs consisting of 166 Portfolios	None

TRUSTEE  AND  OFFICER  INFORMATION 23

Trustee and Officer Information  (continued)

Independent Trustees(a) (continued)
Name Year of Birth(b)	Position(s) Held (Length of Service)(c)	Principal Occupation(s) During Past 5 Years	Number of BlackRock-Advised Registered Investment Companies (“RICs”) Consisting of Investment Portfolios (“Portfolios”) Overseen	Public Company and Other Investment Company Directorships Held During Past 5 Years
Claire A. Walton 1957	Trustee (Since 2016)	Advisory Board Member, Grossman School of Business at the University of Vermont since 2023; Advisory Board Member, Scientific Financial Systems since 2022; General Partner of Neon Liberty Capital Management, LLC since 2003; Chief Operating Officer and Chief Financial Officer of Liberty Square Asset Management, LP from 1998 to 2015; Director, Boston Hedge Fund Group from 2009 to 2018; Director, Massachusetts Council on Economic Education from 2013 to 2015; Director, Woodstock Ski Runners from 2013 to 2022.	28 RICs consisting of 166 Portfolios	None
Interested Trustees(a)(d)
Name Year of Birth(b)	Position(s) Held (Length of Service)(c)	Principal Occupation(s) During Past 5 Years	Number of BlackRock-Advised (“RICs”) Consisting of Investment Portfolios (“Portfolios”) Overseen	Public Company and Other Investment Company Directorships Held During Past 5 Years
Robert Fairbairn 1965	Trustee (Since 2018)	Vice Chairman of BlackRock, Inc. since 2019; Member of BlackRock’s Global Executive and Global Operating Committees; Co-Chair of BlackRock’s Human Capital Committee; Senior Managing Director of BlackRock, Inc. from 2010 to 2019; oversaw BlackRock’s Strategic Partner Program and Strategic Product Management Group from 2012 to 2019; Member of the Board of Managers of BlackRock Investments, LLC from 2011 to 2018; Global Head of BlackRock’s Retail and iShares® businesses from 2012 to 2016.	98 RICs consisting of 266 Portfolios	None
John M. Perlowski(e) 1964	Trustee (Since 2015) President and Chief Executive Officer (Since 2010)	Managing Director of BlackRock, Inc. since 2009; Head of BlackRock Global Accounting and Product Services since 2009; Advisory Director of Family Resource Network (charitable foundation) since 2009.	100 RICs consisting of 268 Portfolios	None

^(a)  The address of each Trustee is c/o BlackRock, Inc., 50 Hudson Yards, New York, NY 10001.

^(b)  Independent Trustees serve until their resignation, retirement, removal or death, or until December 31 of the year in which they turn 75. The Board may determine to extend the terms of Independent Trustees on a case-by-case basis, as appropriate.

^(c)  Following the combination of Merrill Lynch Investment Managers, L.P. (“MLIM”) and BlackRock, Inc. in September 2006, the various legacy MLIM and legacy BlackRock fund boards were realigned and consolidated into three new fund boards in 2007. Furthermore, effective January 1, 2019, three BlackRock Fund Complexes were realigned and consolidated into two BlackRock Fund Complexes. As a result, although the chart shows the year that each Independent Trustee joined the Board, certain Independent Trustees first became members of the boards of other BlackRock-advised Funds, legacy MLIM funds or legacy BlackRock funds as follows: Cynthia A. Montgomery, 1994; Kenneth L. Urish, 1999; Lena G. Goldberg, 2016; Henry R. Keizer, 2016; Donald C. Opatrny, 2015.

^(d)  Mr. Fairbairn and Mr. Perlowski are both “interested persons,” as defined in the 1940 Act, of the Trust based on their positions with BlackRock, Inc. and its affiliates. Mr. Fairbairn and Mr. Perlowski are also board members of the BlackRock Fixed-Income Complex.

^(e)  Mr. Perlowski is also a trustee of the BlackRock Credit Strategies Fund and BlackRock Private Investments Fund.

24 2 0 2 3   BLACK ROCK  ANNUAL  REPORT   TO  SHAREHOLDERS

Trustee and Officer Information  (continued)

Officers Who Are Not Trustees (a)
Name Year of Birth(b)	Position(s) Held (Length of Service)	Principal Occupation(s) During Past 5 Years
Roland Villacorta 1971	Vice President (Since 2022)	Managing Director of BlackRock, Inc. since 2022; Head of Global Cash Management and Head of Securities Lending within BlackRock’s Portfolio Management Group since 2022; Member of BlackRock’s Global Operating Committee since 2022; Head of Portfolio Management in BlackRock’s Financial Markets Advisory Group within BlackRock Solutions from 2008 to 2015; Co-Head of BlackRock Solutions’ Portfolio Analytics Group; previously Mr. Villacorta was Co-Head of Fixed Income within BlackRock’s Risk & Quantitative Analysis Group.
Jennifer McGovern 1977	Vice President (Since 2014)	Managing Director of BlackRock, Inc. since 2016; Director of BlackRock, Inc. from 2011 to 2015; Head of Americas Product Development and Governance for BlackRock’s Global Product Group since 2019; Head of Product Structure and Oversight for BlackRock’s U.S. Wealth Advisory Group from 2013 to 2019.
Trent Walker 1974	Chief Financial Officer (Since 2021)	Managing Director of BlackRock, Inc. since September 2019; Executive Vice President of PIMCO from 2016 to 2019; Senior Vice President of PIMCO from 2008 to 2015; Treasurer from 2013 to 2019 and Assistant Treasurer from 2007 to 2017 of PIMCO Funds, PIMCO Variable Insurance Trust, PIMCO ETF Trust, PIMCO Equity Series, PIMCO Equity Series VIT, PIMCO Managed Accounts Trust, 2 PIMCO-sponsored interval funds and 21 PIMCO-sponsored closed-end funds.
Jay M. Fife 1970	Treasurer (Since 2007)	Managing Director of BlackRock, Inc. since 2007.
Charles Park 1967	Chief Compliance Officer (Since 2014)	Anti-Money Laundering Compliance Officer for certain BlackRock-advised Funds from 2014 to 2015; Chief Compliance Officer of BlackRock Advisors, LLC and the BlackRock-advised Funds in the BlackRock Multi-Asset Complex and the BlackRock Fixed-Income Complex since 2014; Principal of and Chief Compliance Officer for iShares® Delaware Trust Sponsor LLC since 2012 and BlackRock Fund Advisors (“BFA”) since 2006; Chief Compliance Officer for the BFA-advised iShares® exchange traded funds since 2006; Chief Compliance Officer for BlackRock Asset Management International Inc. since 2012.
Lisa Belle 1968	Anti-Money Laundering Compliance Officer (Since 2019)	Managing Director of BlackRock, Inc. since 2019; Global Financial Crime Head for Asset and Wealth Management of JP Morgan from 2013 to 2019; Managing Director of RBS Securities from 2012 to 2013; Head of Financial Crimes for Barclays Wealth Americas from 2010 to 2012.
Janey Ahn 1975	Secretary (Since 2019)	Managing Director of BlackRock, Inc. since 2018; Director of BlackRock, Inc. from 2009 to 2017.

^(a)  The address of each Officer is c/o BlackRock, Inc., 50 Hudson Yards, New York, NY 10001.

^(b)  Officers of the Trust serve at the pleasure of the Board.

Further information about the Trust’s Trustees and Officers is available in the Trust’s Statement of Additional Information, which can be obtained without charge by calling (800) 441-7762.

 Effective December 31, 2022, Joseph P. Platt retired as a Trustee of the Fund.

TRUSTEE  AND  OFFICER  INFORMATION 25

Additional Information

General Information

Quarterly performance, semi-annual and annual reports, current net asset value and other information regarding the Fund may be found on BlackRock’s website, which can be accessed at blackrock.com. Any reference to BlackRock’s website in this report is intended to allow investors public access to information regarding the Fund and does not, and is not intended to, incorporate BlackRock’s website in this report.

Householding

The Fund will mail only one copy of shareholder documents, including prospectuses, annual and semi-annual reports, Rule 30e-3 notices and proxy statements, to shareholders with multiple accounts at the same address. This practice is commonly called “householding” and is intended to reduce expenses and eliminate duplicate mailings of shareholder documents. Mailings of your shareholder documents may be householded indefinitely unless you instruct us otherwise. If you do not want the mailing of these documents to be combined with those for other members of your household, please call the Transfer Agent at (800) 441-7762.

Availability of Quarterly Schedule of Investments

The Fund files its complete schedule of portfolio holdings with the SEC each month on Form N-MFP. The Fund’s reports on Form N-MFP are available on the SEC’s website at sec.gov. The Fund makes portfolio holdings available to shareholders on its website at blackrock.com.

Availability of Proxy Voting Policies, Procedures and Voting Records

A description of the policies and procedures that the Fund uses to determine how to vote proxies relating to portfolio securities and information about how the Fund voted proxies relating to securities held in the Fund’s portfolio during the most recent 12-month period ended June 30 is available without charge, upon request (1) by calling (800) 626-1960; (2) on the BlackRock website at blackrock.com; and (3) on the SEC’s website at sec.gov.

Shareholder Privileges

Account Information

Call us at (800) 441-7762 from 8:00 AM to 6:00 PM ET on any business day to get information about your account balances, recent transactions and share prices. You can also visit blackrock.com for more information.

Automatic Investment Plans

Investor class shareholders who want to invest regularly can arrange to have $50 or more automatically deducted from their checking or savings account and invested in any of the BlackRock funds.

Systematic Withdrawal Plans

Investor class shareholders can establish a systematic withdrawal plan and receive periodic payments of $50 or more from their BlackRock funds, as long as their account balance is at least $10,000.

Retirement Plans

Shareholders may make investments in conjunction with Traditional, Rollover, Roth, Coverdell, Simple IRAs, SEP IRAs and 403(b) Plans.

BlackRock Privacy Principles

BlackRock is committed to maintaining the privacy of its current and former fund investors and individual clients (collectively, “Clients”) and to safeguarding their non-public personal information. The following information is provided to help you understand what personal information BlackRock collects, how we protect that information and why in certain cases we share such information with select parties.

If you are located in a jurisdiction where specific laws, rules or regulations require BlackRock to provide you with additional or different privacy-related rights beyond what is set forth below, then BlackRock will comply with those specific laws, rules or regulations.

BlackRock obtains or verifies personal non-public information from and about you from different sources, including the following: (i) information we receive from you or, if applicable, your financial intermediary, on applications, forms or other documents; (ii) information about your transactions with us, our affiliates, or others; (iii) information we receive from a consumer reporting agency; and (iv) from visits to our websites.

BlackRock does not sell or disclose to non-affiliated third parties any non-public personal information about its Clients, except as permitted by law or as is necessary to respond to regulatory requests or to service Client accounts. These non-affiliated third parties are required to protect the confidentiality and security of this information and to use it only for its intended purpose.

We may share information with our affiliates to service your account or to provide you with information about other BlackRock products or services that may be of interest to you. In addition, BlackRock restricts access to non-public personal information about its Clients to those BlackRock employees with a legitimate business need for the

26 2 0 2 3   BLACK ROCK  ANNUAL  REPORT   TO  SHAREHOLDERS

Additional Information  (continued)

BlackRock Privacy Principles (continued)

information. BlackRock maintains physical, electronic and procedural safeguards that are designed to protect the non-public personal information of its Clients, including procedures relating to the proper storage and disposal of such information.

Fund and Service Providers

Investment Adviser

BlackRock Advisors, LLC

Wilmington, DE 19809

Accounting Agent and Custodian

State Street Bank and Trust Company

Boston, MA 02114

Transfer Agent

BNY Mellon Investment Servicing (US) Inc.

Wilmington, DE 19809

Distributor

BlackRock Investments, LLC

New York, NY 10001

Independent Registered Public Accounting Firm

Deloitte & Touche LLP

Boston, MA 02116

Legal Counsel

Sidley Austin LLP

New York, NY 10019

Address of the Fund

100 Bellevue Parkway

Wilmington, DE 19809

ADDITIONAL  INFORMATION 27

Glossary of Terms Used in this Report

Portfolio Abbreviation

SOFR Secured Overnight Financing Rate

28 2 0 2 3   BLACK ROCK  ANNUAL  REPORT   TO  SHAREHOLDERS

Want to know more?

blackrock.com  |  800-441-7762

This report is intended for current holders. It is not authorized for use as an offer of sale or a solicitation of an offer to buy shares of the Fund unless preceded or accompanied by the Fund’s current prospectus. You could lose money by investing in the Fund. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so. 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 at any time. Performance data quoted represents past performance and does not guarantee future results. Total return information assumes reinvestment of all distributions. Current performance may be higher or lower than the performance data quoted. For current month-end performance information, call (800) 626-1960. The Fund’s current 7-day yield more closely reflects the current earnings of the Fund than the total returns quoted. Statements and other information herein are as dated and are subject to change.

SUMMITMM-04/23-AR

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(b) Not Applicable

Item 2 – Code of Ethics – The registrant (or the “Fund”) has adopted a code of ethics, as of the end of the period covered by this report, applicable to the registrant’s principal executive officer, principal financial officer, principal accounting officer or controller, or persons performing similar functions. During the period covered by this report, the code of ethics was amended to update certain information and to make other non-material changes. During the period covered by this report, there have been no waivers granted under the code of ethics. The registrant undertakes to provide a copy of the code of ethics to any person upon request, without charge, who calls 1-800-441-7762.

Item 3 – Audit Committee Financial Expert – The registrant’s board of directors (the “board of directors”), has determined that (i) the registrant has the following audit committee financial experts serving on its audit committee and (ii) each audit committee financial expert is independent:

Neil A. Cotty

Henry R. Keizer

Kenneth L. Urish

Under applicable securities laws, a person determined to be an audit committee financial expert will not be deemed an “expert” for any purpose, including without limitation for the purposes of Section 11 of the Securities Act of 1933, as a result of being designated or identified as an audit committee financial expert. The designation or identification of a person as an audit committee financial expert does not impose on such person any duties, obligations, or liabilities greater than the duties, obligations, and liabilities imposed on such person as a member of the audit committee and board of directors in the absence of such designation or identification. The designation or identification of a person as an audit committee financial expert does not affect the duties, obligations, or liability of any other member of the audit committee or board of directors.

Item 4 – Principal Accountant Fees and Services

The following table presents fees billed by Deloitte & Touche LLP (“D&T”) in each of the last two fiscal years for the services rendered to the Fund:

	(a) Audit Fees		(b) Audit-Related Fees1		(c) Tax Fees2		(d) All Other Fees
Entity Name	Current     Fiscal Year     End	Previous     Fiscal Year     End	Current     Fiscal Year     End	Previous     Fiscal Year     End	Current     Fiscal Year     End	Previous     Fiscal Year     End	Current     Fiscal Year     End	Previous     Fiscal Year     End
BlackRock Summit Cash Reserves Fund	$28,356	$27,234	$0	$0	$9,900	$9,500	$218	$420

The following table presents fees billed by D&T that were required to be approved by the registrant’s audit committee (the “Committee”) for services that relate directly to the operations or financial reporting of the Fund and that are rendered on behalf of BlackRock Advisors, LLC (the “Investment Adviser” or “BlackRock”) and entities controlling, controlled by, or under common control with BlackRock (not including any sub-adviser whose role is primarily portfolio management and is subcontracted with or overseen by another investment adviser) that provide ongoing services to the Fund (“Affiliated Service Providers”):

2

	Current Fiscal Year End	Previous Fiscal Year End
(b) Audit-Related Fees1	$0	$0
(c) Tax Fees2	$0	$0
(d) All Other Fees3	$2,154,000	$2,098,000

¹ The nature of the services includes assurance and related services reasonably related to the performance of the audit or review of financial statements not included in Audit Fees, including accounting consultations, agreed-upon procedure reports, attestation reports, comfort letters, out-of-pocket expenses and internal control reviews not required by regulators.

² The nature of the services includes tax compliance and/or tax preparation, including services relating to the filing or amendment of federal, state or local income tax returns, regulated investment company qualification reviews, taxable income and tax distribution calculations.

³ Non-audit fees of $2,154,000 and $2,098,000 for the current fiscal year and previous fiscal year, respectively, were paid to the Fund’s principal accountant in their entirety by BlackRock, in connection with services provided to the Affiliated Service Providers of the Fund and of certain other funds sponsored and advised by BlackRock or its affiliates for a service organization review and an accounting research tool subscription. These amounts represent aggregate fees paid by BlackRock and were not allocated on a per fund basis.

(e)(1) Audit Committee Pre-Approval Policies and Procedures:

The Committee has adopted policies and procedures with regard to the pre-approval of services. Audit, audit-related and tax compliance services provided to the registrant on an annual basis require specific pre-approval by the Committee. The Committee also must approve other non-audit services provided to the registrant and those non-audit services provided to the Investment Adviser and Affiliated Service Providers that relate directly to the operations and the financial reporting of the registrant. Certain of these non-audit services that the Committee believes are (a) consistent with the SEC’s auditor independence rules and (b) routine and recurring services that will not impair the independence of the independent accountants may be approved by the Committee without consideration on a specific case-by-case basis (“general pre-approval”). The term of any general pre-approval is 12 months from the date of the pre-approval, unless the Committee provides for a different period. Tax or other non-audit services provided to the registrant which have a direct impact on the operations or financial reporting of the registrant will only be deemed pre-approved provided that any individual project does not exceed $10,000 attributable to the registrant or $50,000 per project. For this purpose, multiple projects will be aggregated to determine if they exceed the previously mentioned cost levels.

Any proposed services exceeding the pre-approved cost levels will require specific pre-approval by the Committee, as will any other services not subject to general pre-approval (e.g., unanticipated but permissible services). The Committee is informed of each service approved subject to general pre-approval at the next regularly scheduled in-person board meeting. At this meeting, an analysis of such services is presented to the Committee for ratification. The Committee may delegate to the Committee Chairman the authority to approve the provision of and fees for any specific engagement of permitted non-audit services, including services exceeding pre-approved cost levels.

(e)(2) None of the services described in each of Items 4(b) through (d) were approved by the Committee pursuant to the de minimis exception in paragraph (c)(7)(i)(C) of Rule 2-01 of Regulation S-X.

(f) Not Applicable

(g) The aggregate non-audit fees, defined as the sum of the fees shown under “Audit-Related Fees,” “Tax Fees” and “All Other Fees,” paid to the accountant for services rendered by the accountant to the registrant, the Investment Adviser and the Affiliated Service Providers were:

3

Entity Name	Current Fiscal Year     End	Previous Fiscal Year     End
BlackRock Summit Cash Reserves Fund	$10,118	$9,920

Additionally, the amounts billed by D&T in connection with services provided to the Affiliated Service Providers of the Fund and of other funds sponsored and advised by BlackRock or its affiliates during the current and previous fiscal years for a service organization review and an accounting research tool subscription were:

Current Fiscal Year     End	Previous Fiscal Year   End
$2,154,000	$2,098,000

These amounts represent aggregate fees paid by BlackRock and were not allocated on a per fund basis.

(h) The Committee has considered and determined that the provision of non-audit services that were rendered to the Investment Adviser and the Affiliated Service Providers that were not pre-approved pursuant to paragraph (c)(7)(ii) of Rule 2-01 of Regulation S-X is compatible with maintaining the principal accountant’s independence.

(i) – Not Applicable

(j) – Not Applicable

Item 5 – Audit Committee of Listed Registrant – Not Applicable

Item 6 – Investments

(a) The registrant’s Schedule of Investments is included as part of the Report to Stockholders filed under Item 1(a) of this Form.

(b) Not Applicable due to no such divestments during the semi-annual period covered since the previous Form N-CSR filing.

Item 7 – Disclosure of Proxy Voting Policies and Procedures for Closed-End Management Investment Companies – Not Applicable

Item 8 – Portfolio Managers of Closed-End Management Investment Companies – Not Applicable

Item 9 – Purchases of Equity Securities by Closed-End Management Investment Company and Affiliated Purchasers – Not Applicable

Item 10 – Submission of Matters to a Vote of Security Holders – There have been no material changes to these procedures.

Item 11 – Controls and Procedures

4

(a) The registrant’s principal executive and principal financial officers, or persons performing similar functions, have concluded that the registrant’s disclosure controls and procedures (as defined in Rule 30a-3(c) under the Investment Company Act of 1940, as amended (the “1940 Act”)) are effective as of a date within 90 days of the filing of this report based on the evaluation of these controls and procedures required by Rule 30a-3(b) under the 1940 Act and Rule 15d-15(b) under the Securities Exchange Act of 1934, as amended.

(b) There were no changes in the registrant’s internal control over financial reporting (as defined in Rule 30a-3(d) under the 1940 Act) that occurred during the period covered by this report that have materially affected, or are reasonably likely to materially affect, the registrant’s internal control over financial reporting.

Item 12 – Disclosure of Securities Lending Activities for Closed-End Management Investment Companies – Not Applicable

Item 13 – Exhibits attached hereto

(a)(2) Section 302 Certifications are attached

(a)(3) Any written solicitation to purchase securities under Rule 23c-1 – Not Applicable

(a)(4) Change in Registrant’s independent public accountant – Not Applicable

(b) Section 906 Certifications are attached

5

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, thereunto duly authorized.

BlackRock Financial Institutions Series Trust

By:	/s/ John M. Perlowski
	John M. Perlowski
	Chief Executive Officer (principal executive officer) of
	BlackRock Financial Institutions Series Trust

Date: June 22, 2023

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.

By:	/s/ John M. Perlowski
	John M. Perlowski
	Chief Executive Officer (principal executive officer) of
	BlackRock Financial Institutions Series Trust

Date: June 22, 2023

By:	/s/ Trent Walker
	Trent Walker
	Chief Financial Officer (principal financial officer) of
	BlackRock Financial Institutions Series Trust

Date: June 22, 2023

6