OPTICAL SEMICONDUCTOR DEVICE

PROBLEM TO BE SOLVED: To provide an optical semiconductor device that improves operation characteristics of a photodetector of an optical semiconductor device and can be integrated with a bipolar transistor and an MOS transistor. SOLUTION: An optical semiconductor device is provided with a photodetector 50 having a light receiving operation part 51 that converts incident light into an electrical current signal and performs an electrical current amplification operation on a P--type semiconductor substrate 1. The photodetector 50 includes: a P--type semiconductor layer 2 that is formed on the P--type semiconductor substrate 1 and has an impurity concentration equal to or smaller than that of the P--type semiconductor substrate 1; an N+-type semiconductor region 8 that is formed on the P--type semiconductor layer 2 and has an impurity concentration higher than that of the P--type semiconductor layer 2; and a p+-type semiconductor region 5 that is selectively formed between the P--type semiconductor substrate 1 and the P--type semiconductor layer 2 and has an impurity concentration higher than the P--type semiconductor substrate 1 and the P--type semiconductor layer 2. COPYRIGHT: (C)2010,JPO&INPIT