The present invention is a semiconductor device which includes: a semiconductor substrate; a BOX film disposed on top of the semiconductor substrate; an active layer disposed on top of the BOX film; a base region disposed proximate to a surface of the active layer; a first main electrode region disposed within the base region; a second main electrode region formed from the surface of the active layer to a surface of the BOX film or protruding through the BOX film, and the second main electrode region being spaced from the base region; a gate insulator film disposed on the surface of the base region; a gate electrode disposed on top of the gate insulator film; a first main electrode connected to the first main electrode region; a second main electrode connected to the second main electrode region; and a ground electrode connected to the semiconductor substrate on an opposite side surface from a surface having the BOX film on the semiconductor substrate.