Patent ID: 7576389

Claim:
A semiconductor device having a trench gate transistor comprising: a groove formed in a semiconductor substrate; a first gate electrode formed in a lower part of the groove with a gate insulation film interposed between the first gate electrode and the semiconductor substrate; side walls which are provided on inner walls in an upper part of the groove located at a position higher than the first gate electrode and which have a bottom area larger than a top area thereof; a second gate electrode formed so as to be in contact with the side walls and a part of the top surface of the first gate electrode; a first diffusion layer which has a first impurity concentration, which is formed on opposite sides of said trench gate transistor, and which has a bottom portion higher than a top portion of said first gate electrode; and a second diffusion layer which has a second impurity concentration higher than the first impurity concentration, which is formed next to said first diffusion layer, and which has a bottom portion higher than a bottom portion of said first gate electrode.