Method of manufacturing a semiconductor device for extracting a signal

Abstract

On the p.sup.- substrate, the n.sup.- epitaxial layer is surrounded and isolated by the p well. In the surface of the n.sup.- epitaxial layer, there is provided the p floating region in the vicinity of the p well, on which the sense electrode is provided. The insulation film and the conductive film are formed on the n.sup.- epitaxial layer between the p well and the p floating region to overlap them. The conductive film and the p floating region serve as a composite field plate, which makes it hard that the surface electric field distribution is influenced by the state of electric charge in the surface and relieves the surface electric field by expanding the depletion layer, which extends from the pn junction between the n.sup.- epitaxial layer and the p well into the n.sup.- epitaxial layer in current blocking state, toward the center of the n.sup.- epitaxial layer. The potential of the p floating region is determined by capacity coupling in the current blocking state and thus the sense voltage characteristics through the sense electrode can be smooth.