A semiconductor device includes a semiconductor substrate of a first conductivity type, including a first main surface and a second main surface opposite to each other. A power semiconductor element includes a first electrode in a first region at the first main surface of the semiconductor substrate, and a second electrode at the second main surface. A current flows between the first electrode and the second electrode. The semiconductor device also includes a guard ring of a second conductivity type, in a second region at the first main surface, at a more outer circumference than the first region. A semi-insulating insulation film covers the second region. A dielectric film in the second region covers the semi-insulating insulation film. A flow block portion in a third region at the first main surface, at a more outer circumference than the second region, prevents a flow out of the dielectric film.