The semiconductor device includes a first transistor and a second transistor formed in a semiconductor substrate. The first transistor includes: a first gate insulating film formed on the semiconductor substrate; and a first gate electrode formed on the first gate insulating film. The second transistor includes: a second gate insulating film formed on the semiconductor substrate; and a second gate electrode formed on the second gate insulating film. The first gate insulating film includes a first insulating material with a first element diffused therein, the second gate insulating film includes the first insulating material, and the amount of the first element contained in the first gate insulating film is greater than the amount of the first element contained in the second gate insulating film.