Abstract: A semiconductor device includes: a p-type active region and an n-type active region which are formed in a semiconductor substrate; a first MISFET including a first gate insulating film formed on the p-type active region and a first gate electrode formed on the first gate insulating film and including a first electrode formation film containing a metal element; and a second MISFET including a second gate insulating film formed on the n-type active region and a second gate electrode formed on the second gate insulating film and including a second electrode formation film. The second electrode formation film contains the same metal element as the first electrode formation film and has an oxygen content higher than the first electrode formation film.