Abstract: Provided is a pressure sensor of semiconductor type, having a semiconductor diaphragm, wherein the diaphragm comprises at least one of thin wall parts and at least one of thick wall parts, and defines therein recesses formed in the lower surface of the diaphragm below the thin wall parts, piezoresistance elements are laid on the upper surface of the diaphragm near the thin wall parts, and a supporting member is sealingly jointed to the thick wall parts at the lower surface of the diaphragm, so that the recesses are sealed and confined so as to prevent high pressure fluid from blowing off when the thin wall part is broken.