In a semiconductor device according to the present invention, a p-type well region disposed in an outer peripheral portion of the power semiconductor device is divided into two parts, that is, an inside and an outside, and a field oxide film having a greater film thickness than the gate insulating film is provided on a well region at the outside to an inside of an inner periphery of the well region. Therefore, it is possible to prevent, in the gate insulating film, a dielectric breakdown due to the voltage generated by the flow of the displacement current in switching.