PURPOSE: To provide a highly precise differential pressure signal and to improve controlling precision of a plant by arranging a thin part forming a differential pressure sensor serving as a main strain sensor on a semiconductor base board.

CONSTITUTION: A composite function type differential pressure sensor chip 1 is installed on a housing 4 via a hollow fixing platform 2. A junction layer 20 is provided on the junction face side between the fixing platform 2 and the sensor chip 1. The sensor chip 1 is provided with a thin part 11, which is formed into a circle or a polygon, in an approximately center of one side surface, while the other side surface and the fixing platform 2 cooperatively form a recessed part, 13, into which one side of the differential pressure to be detected is introduced. In this way, the thin part, 11 works as a strain generating body, which responds to the differential pressure, and serves as a pressure sensitive diaphragm for detecting the differential pressure. On the upper surface of the diaphragm 11, P-type resistors 111-114 are formed. The shape and the thickness of the diaphragm 11, which is formed by a method of anisotropic wet etching or dry etching, are desirably set according to the responding differential pressure.