Patent ID: 8435861

Claim:
A method of manufacturing a semiconductor device comprising: forming isolation regions in a semiconductor substrate to form a first area, a second area and third area which are different from each other; oxidizing a surface of the semiconductor substrate to form a first insulating film covering the first area, the second area, and the third area of the semiconductor substrate; removing portions of the first insulating film lying on the first area and the second area; oxidizing the surface of the semiconductor substrate to form a second insulating film covering the first area and the second area; oxidizing the third area covered with the first insulating film; removing a portion of the second insulating film lying on the second area and the portion of the first insulating film lying on the third area; oxidizing the surface of the semiconductor substrate to form a first gate insulating film covering the second area and the third area; and oxidizing the first area covered with the second insulating film to form a second gate insulating film, the second gate insulating film covering the first area is thicker than the first gate insulating film.