PURPOSE: To provide a semiconductor capacitance type pressure difference sensor having improvded sensitivity by manufacturing an extremely thin silicon substrate having excellent uniformity of thickness with low cost and reproducibility.

CONSTITUTION: A crystal surface of the predetermined orientation, for example, a silicon substrate 11 having the surface index (100) is polished like a mirror surface. The mirror-polished surface of the silicon substrate 11 is etched with anisotropic etchant to form a thin part 13 of the predetermined thickness and obtain an extremely thin silicon substrate. Moreover, a semiconductor capacitance type pressure difference sensor comprises a diaphragm consisting of an extremly thin silicon substrate which displaces depending on pressure and a recessed region to be a gap area of a capacitance detecting portion and is also provided with a pair of integrated glass substrates sandwiching the diaphragm and a fixed electrode for detecting capacitance provided opposed to the diaphragm within the recessed region.