X0306 4 2019-05-08 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 2019-05-08 4 M 0 300 12.16 A 749469 D Common Stock 2019-05-08 4 S 0 300 68.91 D 749169 D Common Stock 2019-05-08 4 M 0 13431 12.16 A 762600 D Common Stock 2019-05-08 4 S 0 13431 68.35 D 749169 D Common Stock 2019-05-08 4 M 0 1593 12.16 A 750762 D Common Stock 2019-05-08 4 S 0 1593 67.41 D 749169 D Common Stock 2019-05-09 4 M 0 2894 12.16 A 752063 D Common Stock 2019-05-09 4 S 0 2894 67.77 D 749169 D Common Stock 2019-05-09 4 M 0 1930 12.16 A 751099 D Common Stock 2019-05-09 4 S 0 1930 66.93 D 749169 D Non-Qualified Stock Option (right to buy) 12.16 2019-05-08 4 M 0 300 0.00 D 2019-08-25 Common Stock 300 80293 D Non-Qualified Stock Option (right to buy) 12.16 2019-05-08 4 M 0 13431 0.00 D 2019-08-25 Common Stock 13431 66862 D Non-Qualified Stock Option (right to buy) 12.16 2019-05-08 4 M 0 1593 0.00 D 2019-08-25 Common Stock 1593 65269 D Non-Qualified Stock Option (right to buy) 12.16 2019-05-09 4 M 0 2894 0.00 D 2019-08-25 Common Stock 2894 62375 D Non-Qualified Stock Option (right to buy) 12.16 2019-05-09 4 M 0 1930 0.00 D 2019-08-25 Common Stock 1930 60445 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 $68.90 to $68.91. 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 $67.89 to $68.78. 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 $66.89 to $67.88. 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 $67.41 to $68.14. 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 $66.35 to $67.33. 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. Options vested at a rate of 25% on 8/25/10 and monthly thereafter until all the options were fully vested on 8/25/13. /s/ Jean Liu For: Clay B. Siegall 2019-05-10