The variations in ID-VD characteristic of 0.8 μm SOINMOS transistors are studied, which are exposed to 60Co γ ray at a dose rate of 50 rad (Si)/s. The results show that the linear kink effects of these samples at each dose level ane not presente due to the optimizations of manufacture process and layout design. The drain voltage that corresponds to the impact ionization induced kink effect, increases, with dose level. An anomalous "Kink" effect in the back gate ID-VSUB characteristics of the partially depleted SOINMOS transistors is observed at a high dose level, which is attributed to interface trap states generated at the buried oxide/silicon film interface during irradiation.