A semiconductor device has a semiconductor substrate of a first conductivity type; first to third high-voltage insulated-gate field effect transistors formed on a principal surface of the semiconductor substrate; a first device isolation insulating film that is formed in the semiconductor substrate and isolates the first high-voltage insulated-gate field effect transistor and the second high-voltage insulated-gate field effect transistor from each other; a second device isolation insulating film that is formed in the semiconductor substrate and isolates the first high-voltage insulated-gate field effect transistor and the third high-voltage insulated-gate field effect transistor from each other; a first impurity diffusion layer of the first conductivity type that is formed below the first device isolation insulating film; and a second impurity diffusion layer of the first conductivity type that is formed below the second device isolation insulating film.