A semiconductor device includes a first N-type region formed in a P-type silicon substrate, trenches formed in the substrate, second N-type regions each formed from at least the bottom of a corresponding one of the trenches into the substrate, these second N-type regions contacting each other to constitute a wiring layer and being also in contact with the first N-type region, and an electrode for applying a predetermined potential to the second N-type regions via the first N-type region. Since a potential is supplied to the wiring layer formed in the substrate via the first N-type region, no special design, such as formation of a terminal trench, is required. A potential can be easily supplied to the wiring layer formed in the semiconductor substrate, and the device can be easily fabricated.