A semiconductor device includes a semiconductor region, deep trenches, a dielectric film, a conductive material, an interlayer insulating film, and a metal interconnection. The semiconductor region has a first conductivity type in a silicon substrate. The deep trenches are disposed in the semiconductor region. The dielectric film is disposed on sidewalls of the deep trenches. The conductive material is disposed on the dielectric film. The interlayer insulating film is disposed on upper surface portions of the deep trenches to create a void inside each of the deep trenches. The metal interconnection is disposed on the interlayer insulating film.