A semiconductor device, including: a first group of transistors formed on a semiconductor substrate; and a second group of transistors formed on the semiconductor substrate, each of which is lower in operating voltage than each of the transistors in the first group; wherein each of the transistors in the first group includes a first gate electrode formed on the semiconductor substrate through a first gate insulating film, and a silicide layer formed on the first gate electrode; each of the transistors in the second group includes a second gate electrode formed in a trench for gate formation, formed in an insulating film above the semiconductor substrate, through a second gate insulating film; and a protective film is formed so as to cover the silicide layer on each of the first gate electrodes of the first group of transistors.