Effects of switched bias on the radiation response of metal‐oxide‐semiconductor (MOS) devices have been investigated. Transistors with 50‐nm gate oxides were irradiated at +10‐V bias to create a large trapped‐hole density in the oxide. Irradiation was continued under varying negative and positive biases. Very little radiation‐induced charge neutralization is observed at biases <−10 V for these devices. However, significant trapped‐hole neutralization is observed at biases from −10 to 0 V, with a broad maximum in neutralization rate from −6 to −1 V. The peak charge neutralization rate is approximately equal to the rate of trapped‐hole buildup under positive bias. This establishes an upper bound on the rate of radiation‐induced charge neutralization, and demonstrates that, under peak neutralization conditions, the effective cross section for the capture of radiation‐induced electrons by a filled hole trap is similar to the effective cross section for capture of a hole by an empty trap. Interface traps are found to build up at approximately the same rate when the oxide electric field at the Si/SiO2interface is positive, regardless of the field direction in the bulk of the oxide. This suggests that near‐interfacial hydrogen may play a key role in interface‐trap buildup in MOS devices.