A semiconductor device comprises a first MIS transistor and a second MIS transistor. The first MIS transistor includes a first gate insulating film formed on a first active region, and a first gate electrode formed on the first gate insulating film. The second MIS transistor includes a second gate insulating film formed on a second active region and made of an insulating material different from that of the first gate insulating film, and a second gate electrode formed on the second gate insulating film. Upper regions of the first gate electrode and the second gate electrode are electrically connected to each other on the isolation region located between the first active region and the second active region, and lower regions thereof are separated from each other with a sidewall insulating film made of the same insulating material as that of the first gate insulating film being interposed therebetween.