X0306 4/A 2021-04-13 2021-04-14 0001049502 MKS INSTRUMENTS INC MKSI 0001842711 Gitin Mark Milton C/O MKS INSTRUMENTS, INC. 2 TECH DRIVE, SUITE 201 ANDOVER MA 01810 1 SVP & GM, L&M Division Common Stock 2021-04-13 4 F 0 317 186.52 D 4733.054 D This transaction was effected pursuant to a Rule 10b5-1 trading plan previously adopted by the reporting person. The original Form 4 filed on April 14, 2021 (the "Original Form 4"), is hereby amended solely to correct an error in the number of shares of common stock of MKS Instruments, Inc. that were withheld from the reporting person for the payment of tax liabilities. Please note that the 70 additional shares that should have been reported as withheld for the payment of tax liabilities on the Original Form 4 were included in the reporting person's holdings in a subsequent Form 4 filed on April 21, 2021. The reporting person will exclude these shares from the reporting person's holdings in future filings. /s/ M. Kathryn Rickards, attorney-in-fact 2021-04-22