The effects of high-frequency AC bias on the ionizing radiation response of MOSFETs are studied. Radiation-induced interface traps are annealed out during irradiation and postirradiation annealing when an AC bias is applied with a zero offset voltage. In addition, the recovery of 40-MHz-biased devices agreed with that of 860-MHz-biased ones for the same total number of alternating cycles of AC gate bias voltage. It is concluded that an alternating transition between inversion and accumulation caused by high-frequency AC bias is responsible, and the total number of transition cycles may be relevant for the annealing of radiation-induced interface traps. >