Effect of gamma and proton irradiation on threshold voltage shift ΔV(T) for n-channel MOSFET has been studied. For MOSFET with zero gate bias during gamma irradiation the shift ΔV(T) is linear with dose D(γ) (up to doses of 10 Gy) and the sensitivity ΔV(T)/D(γ) is approximately 120 mV · Gy-1. The sensitivity of MOSFETs with positive gate bias V(g) during irradiation varies as V(g)(2/3) and no saturation is observed up to breakdown voltage. n-MOSFETs with bias of 100 V have the sensitivity of approximately 5 V · Gy-1. When n-MOSFETs are irradiated with 50 MeV protons the shift ΔV(T) varies as D(p)0.67 (for proton doses D(p) ranged from 0.2 to 900 Gy). The positive charge storage in oxide is shown to contribute mainly to the radiation sensitivity of n-MOSFETs investigated.