X0306 4 2013-03-05 0001097864 ON SEMICONDUCTOR CORP ONNN 0001368095 Mahoney Robert Charles 5005 EAST MCDOWELL ROAD PHOENIX AZ 85008 1 Exec VP Sales & Marketing Common 2013-03-05 4 F 0 9785.0000 8.0100 D 123940.0000 D Common 2013-03-06 4 S 0 10000.0000 8.1304 D 113940.0000 D This disposition transactions represents shares withheld by the Issuer in connection with the March 5, 2012 restricted stock units award to the Reporting Person under the Issuer's Amended and Restated Stock Incentive Plan. On March 5, 2013, certain of these units vested. These shares were withheld to satisfy the Reporting Person's withholding obligations for various taxes and similar items. The Issuer will pay these taxes on behalf of the Reporting Person. This disposition transaction was executed in multiple trades at prices ranging from $8.13 to $8.1306. The prices reported above reflects the weighted average sale price. The Reporting Person hereby undertakes to provide, upon request, to the SEC staff, the Issuer, or a security holder of the Issuer, full information regarding the number of shares and process at which the transaction was effected. Judith A. Boyle is signing on behalf of the Reporting Person pursuant to a Power of Attorney attached hereto as an Exhibit. mahoney2012poa.txt Judith A. Boyle, Attorney-in-Fact 2013-03-07