A semiconductor device includes a first main electrode; a second main electrode; a first semiconductor region of a first conductivity type; a second semiconductor region of the first conductivity type; a third semiconductor region of a second conductivity type arranged between the first semiconductor region and the second semiconductor region; and a depletion layer suppression region arranged inside of the third semiconductor region and being configured to suppress a spread of a depletion layer extending in the third semiconductor region when a reverse bias voltage is applied between the second semiconductor region and the third semiconductor region. The third semiconductor region includes a shortest region where a distance between a first boundary surface and a second boundary surface is shortest, and the shortest region includes a region where the depletion layer suppression region does not exist between the first boundary surface and the second boundary surface.