A semiconductor device includes a first MOS structure portion that includes, as its elements, a semiconductor substrate of a first conductivity type, a first semiconductor layer of the first conductivity type, a first second-semiconductor-layer of a second conductivity type, first semiconductor regions of the first conductivity type, and first gate insulating films, and a second MOS structure portion that includes, as its elements, the substrate, the first semiconductor layer, a second second-semiconductor-layer, second first-semiconductor-regions of the first conductivity type, and second gate insulating films. First and second portions include all of the elements of the first and second MOS structure portions other than the first and second first-semiconductor-regions and the first and second gate insulating films, respectively. A structure of one of the elements of the first portion is not identical to a structure of a corresponding element of the second portion.