A trench gate semiconductor device including: a semiconductor layer having a first conductivity type; a first diffusion region having a second conductivity type having a planar structure on the semiconductor layer; a second diffusion region having the first conductivity type positioned selectively on the first diffusion region; a gate electrode provided via a gate insulation film in each first trench facing the second diffusion region and penetrating through the first diffusion region to reach the semiconductor layer; a first semiconductor region of the second conductivity type provided at a position, in the semiconductor layer, apart in a lateral direction from the first diffusion region; a second semiconductor region of the second conductivity type provided at a position, in the first diffusion region, between the adjacent first trenches; and a main electrode in contact with the semiconductor layer and the second diffusion region.