Statement of Changes in Beneficial Ownership (4)

FORM 4

[ ] Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES

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3235-0287

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Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940

1. Name and Address of Reporting Person * Burke Kathleen Flaherty	2. Issuer Name and Ticker or Trading Symbol MKS INSTRUMENTS INC [ MKSI ]	5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director                    _____ 10% Owner __X__ Officer (give title below)    _____ Other (specify below) Sr. VP, GC & Secretary
(Last)          (First)          (Middle) C/O MKS INSTRUMENTS, INC., 2 TECH DRIVE, SUITE 201	3. Date of Earliest Transaction (MM/DD/YYYY) 2/16/2021
(Street) ANDOVER, MA 01810 (City)        (State)        (Zip)	4. If Amendment, Date Original Filed (MM/DD/YYYY)	6. Individual or Joint/Group Filing (Check Applicable Line) _X _ Form filed by One Reporting Person ___ Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security (Instr. 3)	2. Trans. Date	2A. Deemed Execution Date, if any	3. Trans. Code (Instr. 8)		4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	2/16/2021		M		1071.322	A	(1)	35615.896	D
Common Stock	2/16/2021		M		1050.315	A	(1)	36666.211	D
Common Stock	2/16/2021		M		1290.83	A	(1)	37957.041	D
Common Stock	2/16/2021		M		1574.183	A	(1)	39531.224	D
Common Stock	2/16/2021		M		1844	A	(1)	41375.224	D
Common Stock	2/16/2021		M		1280	A	(1)	42655.224	D
Common Stock	2/16/2021		F(2)		3225	D	$172.20	39430.224	D

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivate Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Trans. Date	3A. Deemed Execution Date, if any	4. Trans. Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Restricted Stock Unit	(1)	2/16/2021		A		3048.78		(3)	(3)	Common Stock	3048.78	(1)	24633.229	D
Restricted Stock Unit	(1)	2/16/2021		M			1071.322	(4)	(4)	Common Stock	1071.322	(1)	23561.907	D
Restricted Stock Unit	(1)	2/16/2021		M			1050.315	(5)	(5)	Common Stock	1050.315	(1)	22511.592	D
Restricted Stock Unit	(1)	2/16/2021		M			1290.83	(6)	(6)	Common Stock	1290.83	(1)	21220.762	D
Restricted Stock Unit	(1)	2/16/2021		M			1574.183	(7)	(7)	Common Stock	1574.183	(1)	19646.579	D
Restricted Stock Unit	(1)	2/16/2021		M			1844	(8)	(8)	Common Stock	1844	(1)	17802.579	D
Restricted Stock Unit	(1)	2/16/2021		M			1280	(9)	(9)	Common Stock	1280	(1)	16522.579	D

Explanation of Responses:
(1)	Each restricted stock unit (RSU) represents the contingent right to receive one share of common stock of MKS Instruments, Inc.
(2)	This transaction was effected pursuant to a Rule 10b5-1 trading plan previously adopted by the reporting person.
(3)	These RSUs vest in three equal annual installments commencing on February 15, 2022, provided that if, in any vesting year, February 15th is not a business day, such vesting shall occur on the next business day.
(4)	These RSUs were subject to performance criteria, the achievement of which was determined on January 28, 2019, and thereafter vest in three equal annual installments beginning on February 15, 2019, provided that if, in any vesting year, February 15th is not a business day, such vesting shall occur on the next business day.
(5)	These RSUs vest in three equal annual installments commencing on February 15, 2019, provided that if, in any vesting year, February 15th is not a business day, such vesting shall occur on the next business day.
(6)	These RSUs were subject to performance criteria, the achievement of which was determined on January 27, 2020, and thereafter vest in three equal installments beginning on February 15, 2020, provided that if, in any vesting year, February 15th is not a business day, such vesting shall occur on the next business day.
(7)	These RSUs vest in three equal annual installments commencing on February 15, 2020, provided that if, in any vesting year, February 15th is not a business day, such vesting shall occur on the next business day.
(8)	These RSUs were subject to performance criteria, the achievement of which was determined on January 25, 2021, and thereafter vest in three equal annual installments beginning on February 15, 2021, provided that if, in any vesting year, February 15th is not a business day, such vesting shall occur on the next business day.
(9)	These RSUs vest in three equal annual installments commencing on February 15, 2021, provided that if, in any vesting year, February 15th is not a business day, such vesting shall occur on the next business day.

Reporting Owners
Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
Burke Kathleen Flaherty C/O MKS INSTRUMENTS, INC. 2 TECH DRIVE, SUITE 201 ANDOVER, MA 01810			Sr. VP, GC & Secretary

Signatures
/s/ M. Kathryn Rickards, attorney-in-fact		2/17/2021
**Signature of Reporting Person		Date