PURPOSE: To obtain a pressure sensor excellent in sensor characteristics by enhancing the machining accuracy of a diaphragm.

CONSTITUTION: A silicon wafer is subjected, on one side thereof, to dry etching to form a circular gap 4 and a protrusion 15 on the peripheral edge thereof. The silicon wafer is subjected, on the other side thereof, to anisotropic etching to form a thin film part 12 wider than the gap 4 thus producing a silicon frame 1 in which a circular diaphragm 2 is formed. A glass cover 3 is applied to the upper surface of the frame 1 and anode bonded thereto thus producing a pressure sensor A. Since the position, size and shape of the diaphragm 2 are determined by the circular gap 4 formed through dry etching, a highly accurate diaphragm 2 can be produced with regard to the position and size.