A semiconductor device includes a substrate having an active layer, an element region provided in the active layer, a P-type semiconductor region provided in the element region, and first and second N-type semiconductor regions provided in the element region, located on the sides of the P-type semiconductor region, respectively and spaced in a first direction. The device has an N-type MOS transistor and first and second P-type MOS transistors. The N-type MOS transistor has a first gate electrode provided on the P-type semiconductor region. The first P-type MOS transistor has a second gate electrode provided on the first N-type semiconductor region. The second P-type MOS transistor has a third gate electrode provided on the second N-type semiconductor region.