The　combined　impact　of　single　event　effect　(SEE)　and　total　ion　dose　(TID)　on　Si-based　radiation-hardened　Vertical　Double-diffused　Metal-Oxide-Semiconductor　(VDMOS)　Field-Effect　Transistor　(VDMO-SFET)　is　investigated　in　this　letter.　As　previous　research　of　VDMOS　on　TID　effect　and　SEE　carried　out　separately,　in　fact,　the　combined　impact　could　degrade　the　device　performance　more　seriously,　because　of　the　greater　numbers　of　oxide-trapped　charges　and　interface　states　generated,　which　is　more　pronounced　during　multiple　gamma　irradiation　and　post-irradiation　annealing.　This　phenomenon　indicates　that　SEE　is　not　only　a　transient　effect,　influencing　whether　the　devices　can　be　driven　to　failure,　but　also　a　potential　threat　to　the　long-term　reliability　of　MOSFETs　used　in　aerospace　applications.