To provide a semiconductor device, for which the light receiving sensitivity and frequency characteristics of a photodetector especially to the light of a short wavelength are improved, and simultaneously realizing desired performance for a semiconductor element other than the photodetector, and to provide its manufacturing method.

A semiconductor substrate 14 is constituted of a first conductivity-type semiconductor substrate 11 and a second conductivity-type semiconductor layer 13, and the thickness of the semiconductor layer 13 in the light receiving part of a photodiode 27 is made smaller than the thickness of the semiconductor layer 13 in a bipolar transistor 28. Thus, an element structure, such as the distance to a depletion layer near the joining boundary of the semiconductor substrate 11 and the semiconductor layer 13 from the surface of the light-receiving part of the photodiode 27 and the element structure, such as the thickness of the semiconductor layer 13 in the bipolar transistor 28, are optimized independently of each other.