A semiconductor device includes a high voltage NMOS transistor formation region defined by an element isolation insulating film, a CMOS transistor formation region defined by an element isolation insulating film, and a substrate contact portion. The substrate contact portion is formed in a region of a semiconductor substrate that is positioned between the high voltage NMOS transistor formation region and the element isolation insulating film so as to reach from the main surface side to a position deeper than the bottom of the element isolation insulating film. The substrate contact portion is in contact with the semiconductor substrate from a depth over a depth.