A semiconductor device includes: a first semiconductor layer of a first conductivity type; an insulation layer on the first semiconductor layer; a second semiconductor layer in the insulation layer; an active element in the second semiconductor layer; a first semiconductor region on the first semiconductor layer and of a second conductivity type; a second semiconductor region in the first semiconductor region and of the second conductivity type with a higher impurity concentration than the first semiconductor region; a first conductor in a through hole in the insulation layer and connected to the second semiconductor region; a second conductor above or within the insulation layer, the second conductor surrounding the first conductor such that an outside edge thereof is outside the second semiconductor region; a third conductor connecting the first and second conductors; and a fourth conductor connected to the first semiconductor layer.