Patent ID: 7834407

Claim:
A semiconductor device comprising: (a) a field-effect transistor having a trench gate structure with a dummy gate electrode, the field-effect transistor comprising: a drain region of the field effect transistor disposed over a semiconductor substrate; a channel forming region of the field-effect transistor disposed over the drain region; a source region of the field-effect transistor disposed over the channel forming region; a trench reaching the drain region from an upper surface of the source region; a first insulating film disposed in the trench and disposed at a lower part of the trench; a first conductive film disposed over the first insulating film in the trench and disposed at the lower part of the trench, the first conductive film serving as the dummy gate electrode; a gate insulating film of the field-effect transistor disposed over the first insulating film in the trench and disposed at a upper part of the trench; a gate electrode of the field-effect transistor disposed over the gate insulating film in the trench and disposed at the upper part of the trench, wherein the gate electrode and the first conductive film are separately disposed in the trench in which a second insulating film is disposed between the gate electrode and the first conductive film, and wherein a thickness of the gate insulating film is less than a thickness of the first insulating film; and (b) a protective diode including a second conductive film which is formed by same film layer as the first conductive film, wherein the field-effect transistor and the protective diode are formed over the same semiconductor substrate.