To obtain a semiconductor differential pressure detector excellent in the linearity of pressure and output even in low pressure region with high productivity by forming a reinforcing layer covering a region where a strain gauge is formed and a supporting part.

A thin diaphragm part 2 and a thick supporting part 3 surrounding the thin diaphragm part 2 are provided on a semiconductor substrate 1 and a strain gauge 4 is formed of a piezoelectric resistor element at the diaphragm part 2. When a reinforcing layer 6 is formed covering at least a part of the region of the diaphragm part 2 where the strain gauge 4 is formed and the supporting part 3, strength is enhanced at the region of the diaphragm part 2 where the strain gauge 4 is formed and highly accurate machining can be carried out easily while keeping linearity in the relationship of pressure and output even in case of low pressure measurement. Furthermore since the reinforcing layer 6 is provided on the surface of the semiconductor substrate 1 where the strain gauge 4 is formed, the strain gauge 4 and the like can be protected.