Gamma‐ray irradiation into vertical type n‐channel hexagonal (4H)‐silicon carbide (SiC) metal‐oxide‐semiconductor field effect transistors (MOSFETs) was performed under various gate biases. The threshold voltage for the MOSFETs irradiated with a constant positive gate bias showed a large negative shift, and the shift slightly recovered above 100 kGy. For MOSFETs with non‐ and a negative constant biases, no significant change in threshold voltage, Vth, was observed up to 400 kGy. By changing the gate bias from positive bias to either negative or non‐bias, the Vth significantly recovered from the large negative voltage shift induced by 50 kGy irradiation with positive gate bias after only 10 kGy irradiation with either negative or zero bias. It indicates that the positive charges generated in the gate oxide near the oxide–SiC interface due to irradiation were removed or recombined instantly by the irradiation under zero or negative biases.

Radiation response of vertical structure hexagonal (4H) silicon carbide (SiC) power metal–oxide–semiconductor field effect transistors (MOSFETs) was investigated up to 5.8 MGy. The drain current–gate voltage curves for the MOSFETs shifted from positive to negative voltages due to irradiation. However, the drain current–gate voltage curve shifts for the MOSFETs irradiated at 150 °C was smaller than those irradiated at room temperature. Thus, the shift of threshold voltage due to irradiation was suppressed by irradiation at 150 °C. No significant change or slight decrease in subthreshold voltage swing for the MOSFETs irradiated at 150 °C was observed. The value of channel mobility increased due to irradiation, and the increase was enhanced by irradiation at 150 °C comparing to irradiation at RT.

The response of hexagonal (4H) silicon carbide (SiC) power metal–oxide–semiconductor field effect transistors (MOSFETs) to gamma-ray irradiation was investigated under elevated temperature and humid conditions. The shift in drain current–gate voltage (I D–V G) curves towards negative voltages and the leakage of I D with a current hump due to elevated temperature irradiation were suppressed under high humidity conditions relative to dry conditions. This result can be explained in terms of the reduction in trapped oxide charge and oxide–SiC interface traps generated by irradiation due to the humid conditions. In addition, during irradiation at elevated temperature in humid conditions, electron traps at the oxide–SiC interface obviously decrease at doses above 100 kGy.