The relation between the threshold voltage shift of BF+2 implanted Si-gate PMOSFET and the total γ-irradiation dose has been systematically studied,and the mechanism of γ-irradiation hardening for BF+2 implantation has also been analyzed in detail.The studies show that BF+2 implantation has a strong suppression for the threshold voltage shift of BF+2 implanted Si-gate PMOSFET under γ-irradiation;optimum BF+2 implantation dose in the hardened Si-Gate PMOSFET ranges from 5×1014—2×1015cm-2;F atoms distributed at SiO2/Si interface,which suppress the oxide-trap charges and interface-trap charges produced under γ-irradiation,may be the main origin of BF+2-implanted and hardened Si-gate PMOSFET.