X0306 4 2017-05-11 0001049502 MKS INSTRUMENTS INC MKSI 0001414656 Lee John Tseng-Chung 2 TECH DRIVE ANDOVER MA 01810 1 Sr. VP & COO Common Stock 2017-05-11 4 M 0 3557.874 A 3558.627 D Common Stock 2017-05-11 4 F 0 1674 80.50 D 1884.627 D Restricted Stock Unit 2017-05-11 4 M 0 3557.874 D Common Stock 3557.874 25294.433 D Each restricted stock unit represents the contingent right to receive one share of common stock of MKS Instruments, Inc. This transaction was effected pursuant to a Rule 10b5-1 trading plan previously adopted by the reporting person. These RSUs originally were scheduled to vest in two equal installments based on the Company's achievement of certain performance criteria for the period ending June 30, 2017 and June 30, 2018. On May 10, 2017, the Compensation Committee accelerated in full the vesting of these RSUs to May 11, 2017 as a result of the Company's 100% achievement of the performance criteria. /s/ M. Kathryn Rickards, attorney-in-fact 2017-05-12