A semiconductor device provides reduced size and increased performance, and includes a semiconductor layer having a surface layer including first and second semiconductor regions connected to first and second potentials, respectively; a third semiconductor region provided inside the first semiconductor region and connected to a third potential; a fourth semiconductor region provided inside the second semiconductor region and connected to the third potential; a plurality of a first element provided in each of the first, second, third, and fourth semiconductor regions; a first isolation region provided between and in contact with the first and second semiconductor regions, electrically connected to the semiconductor layer, and connected to a fourth potential; and a second isolation region which encloses the periphery of and maintains a withstand voltage of the first and second semiconductor regions. The third and fourth potentials are lower than the second potential, which is lower than the first potential.