A semiconductor device is provided with a SOI substrate including a semiconductor substrate, a BOX layer on the semiconductor substrate, and a semiconductor layer on the BOX layer, a multilayer wiring formed over a main surface of the SOI substrate, and an inductor comprised of the multilayer wiring. In a region located below the inductor, the BOX layer and the semiconductor layer are separated into a plurality of regions by an element isolation portion, and a dummy gate electrode is formed on a part of the semiconductor layer, which is located in each of the plurality of regions, via a dummy gate insulating film.