Patent ID: 7804146

Claim:
A semiconductor device comprising: a first transistor having a first gate insulating film formed on a first device region of a semiconductor substrate and a first gate electrode formed on the first gate insulating film, the first gate insulating film being made of silicon oxynitride; a second transistor having a second gate insulating film formed on a second device region of the semiconductor substrate and a second gate electrode formed on the second gate insulating film, the second gate insulating film being made of silicon oxynitride; and a third transistor having a third gate insulating film formed on a third device region of the semiconductor substrate and a third gate electrode formed on the third gate insulating film, wherein an average of a nitrogen concentration is higher in the first gate insulating film than in the second gate insulating film, the first transistor and the third transistor are N-type MOS transistors, the second transistor is a P-type MOS transistor, and the first gate insulating film has a physical thickness greater than the second gate insulating film and smaller than the third gate insulating film.