Method of manufacturing a semiconductor photodetector device by removing the semiconductor substrate on one surface after forming the light-transmitting layer on the opposing surface

A semiconductor photodetector device (PD1) comprises a multilayer structure (LS1) and a glass substrate (1) optically transparent to incident light. The multilayer structure includes an etching stop layer (2), an n-type high-concentration carrier layer (3), an n-type light-absorbing layer (5), and an n-type cap layer (7) which are laminated. A photodetecting region (9) is formed near a first main face (101) of the multilayer structure, whereas a first electrode (21) is provided on the first main face. A second electrode (27) and a third electrode (31) are provided on a second main face (102). A film (10) covering the photodetecting region and first electrode is formed on the first main face. A glass substrate (1) is secured to the front face (10a) of this film.