A semiconductor device of the present invention includes, in a region 1C, a top electrode made by a semiconductor layer of an SOI substrate, a capacitive insulating film made by an insulating layer, a bottom electrode made by a supporting board, and a lead part (a high-concentration impurity region of an n type) of the bottom electrode coupled to the supporting board. An SOI transistor in a region 1B is formed over a main surface of the semiconductor layer over the insulating layer as a thin film, and threshold voltage can be adjusted by applying a voltage to a well arranged on the rear face side of the insulating layer.