A semiconductor device includes one or more transistor cells mounted on a first conductive type silicon carbide (SiC) substrate, wherein each of the transistor cells includes a second conductive type wall region formed on a first surface of the SiC substrate, a first conductive type source region formed in the wall region, a gate electrode formed with a gate insulating film; a source electrode formed in such a way as to be brought into contact with the source region, and a drain electrode formed on a second surface of the SiC substrate. The semiconductor device further includes a second conductive type region located close to an outside of an outermost cell of the transistor cells, the second conductive type region surrounding the wall region and being insulated from both of the gate electrode and the source electrode.