A transistor that forms an integrated circuit, a photo detector and a micromirror are mounted on the same semiconductor substrate in an optical semiconductor device of the present invention, which has an antireflection film that is formed on the photo detector, a first insulating film which is formed on the antireflection film and in which an opening is created in the state where the antireflection film is exposed, and an etching stopping film which is formed on the first insulating film and which has been left in the periphery around the opening in the first insulating film on the antireflection film and in the periphery around the portion above the micromirror.