PURPOSE: To provide a semiconductor device which can effectively prevent deterioration due to irradiation of radiant rays like X-rays.

CONSTITUTION: When a Vcc power supply is cut off by the pause of operation of a MOS transistor 11, a gate terminal 14 is connected with a power supply 17 via a switch 15, a positive DC power supply is applied to the gate terminal of the transistor 11 by connecting a drain terminal 12 to a ground voltage via a switch 16, and the gate oxide film electric field of the transistor is made higher than or equal to about 3MV/cm. Thereby even if the irradiation of radiant rays like X-rays is generated at the time of the Vcc power source disconnection wherein the operation is interrupted, generation of noize trap can be largely restrained, and generation of positive fixed charge (SiO3+) can be simultaneously restrained.