PURPOSE: To unnecessitate the positioning of super high accuracy by a method wherein a supporting base composed of poly Si is formed on an insulation film, and a movable beam composed of poly Si is supported thereon.

CONSTITUTION: A fixed electrode layer 13 is formed on the surface of the semiconductor substrate 11 by a diffused layer 14 of the reverse conductive semiconductor as the substrate 11 or by a conductive thin film. Next, the surface of the substrate 11 is coated with the alkali etching resistant insulation film 12, and the supporting base 14 composed of alkali etching poly Si is formed at a fixed position on the insulation film. Then, the movable beam composed of alkali etching resistant poly Si doped with a P type impurity 15 at high density is so constructed on this supporting base as to be supported in an integral body.