X0306 4 2019-04-08 0 0001060736 SEATTLE GENETICS INC /WA SGEN 0001167496 SIEGALL CLAY B 21823 30TH DRIVE SE BOTHELL WA 98021 1 1 0 0 President and CEO Common Stock 2019-04-08 4 M 0 8807 12.16 A 757976 D Common Stock 2019-04-08 4 S 0 8807 79.77 D 749169 D Common Stock 2019-04-08 4 M 0 8541 12.16 A 757710 D Common Stock 2019-04-08 4 S 0 8541 79.05 D 749169 D Common Stock 2019-04-08 4 M 0 2800 12.16 A 751969 D Common Stock 2019-04-08 4 S 0 2800 78.00 D 749169 D Non-Qualified Stock Option (right to buy) 12.16 2019-04-08 4 M 0 8807 0.00 D 2019-08-25 Common Stock 8807 91934 D Non-Qualified Stock Option (right to buy) 12.16 2019-04-08 4 M 0 8541 0.00 D 2019-08-25 Common Stock 8541 83393 D Non-Qualified Stock Option (right to buy) 12.16 2019-04-08 4 M 0 2800 0.00 D 2019-08-25 Common Stock 2800 80593 D Amount of securities beneficially owned following reported transactions includes restricted stock units subject to vesting. The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 trading plan. Reflects sales of common stock executed in multiple transactions at prices ranging from $79.49 to $80.04. The price reported reflects the weighted average sale price. The Reporting Person hereby undertakes to provide upon request by the Securities and Exchange Commission staff, the Issuer or a security holder of the Issuer full information regarding the number of shares and prices at which the sales were effected. Reflects sales of common stock executed in multiple transactions at prices ranging from $78.49 to $79.48. The price reported reflects the weighted average sale price. The Reporting Person hereby undertakes to provide upon request by the Securities and Exchange Commission staff, the Issuer or a security holder of the Issuer full information regarding the number of shares and prices at which the sales were effected. Reflects sales of common stock executed in multiple transactions at prices ranging from $77.47 to $78.42. The price reported reflects the weighted average sale price. The Reporting Person hereby undertakes to provide upon request by the Securities and Exchange Commission staff, the Issuer or a security holder of the Issuer full information regarding the number of shares and prices at which the sales were effected. Shares vested at a rate of 25% on 8/25/10 and monthly thereafter until all the shares were fully vested on 8/25/13. By: /s/ Jean Liu For: Clay B. Siegall 2019-04-10