A semiconductor device wherein the same metal gate material is used for both an n-channel CMOS transistor and a p-channel CMOS transistor and a manufacturing method therefor are disclosed. The n-channel transistor includes an impurity region, a first gate laminated body that has a gate oxide film and a gate electrode but does not have a gate electrode sidewall insulating film, and a first silicon nitride film that has a tensile stress and covers the surface of a semiconductor substrate and the first gate laminated body. The p-channel transistor includes an impurity region; a second gate laminated body that has a gate oxide film, a gate electrode, and a gate electrode sidewall insulating film; and a second silicon nitride film that has a compressive stress and covers the surface of the semiconductor substrate and the second gate laminated body.