A complementary semiconductor device includes a semiconductor substrate, a first semiconductor region formed on a surface of the semiconductor substrate, a second semiconductor region formed on the surface of the semiconductor substrate apart from the first semiconductor region, an n-MIS transistor having a first gate insulating film including La and Al, formed on the first semiconductor region, and a first gate electrode formed on the gate insulating film, and a p-MIS transistor having a second gate insulating film including La and Al, formed on the second semiconductor region, and a second gate electrode formed on the gate insulating film, an atomic density ratio Al/La in the second gate insulating film being larger than an atomic density ratio Al/La in the first gate insulating film.