A semiconductor device includes the following elements. A semiconductor substrate has a device formation region. The device formation region is defined by first and second device isolation regions which extend in first and second directions, respectively. The device formation region has a first gate groove which extends in the second direction. A first gate insulating film is disposed in a lower portion of the first gate groove. A first gate electrode is disposed on the first gate insulating film. The first gate electrode is disposed in the lower portion of the first gate groove. A buried insulating film is disposed over the first gate electrode. The buried insulating film is disposed in an upper portion of the first gate groove.