A semiconductor device includes a semiconductor substrate of a first conductivity type, a first insulating film region that is embedded in a trench formed on the semiconductor substrate, a gate electrode that covers a lower surface of the first insulating film region, and a gate insulating film that is provided between the gate electrode and the semiconductor substrate. The semiconductor device further includes a first diffusion region that covers a first side surface of the first insulating film region, a second diffusion region that covers a second side surface of the first insulating film region, and a third diffusion region that covers an upper surface of the second diffusion region. A selective element includes a field-effect transistor that is constituted by the gate electrode, the first diffusion region, and the second diffusion region, and a bipolar transistor that is constituted by the substrate and the second and third diffusion regions.