An optical semiconductor device includes a first light receiving region and a second light receiving region provided on a substrate and the first and second light receiving regions include light receiving elements, respectively. A first anti-reflection film is formed in the first light receiving region of the substrate and a second anti-reflection film is formed in the second light receiving region of the substrate. The reflectance of the first anti-reflection film for a first wavelength range of light is lower than the reflectance of the second anti-reflection film for the first wavelength range of light and the reflectance of the second anti-reflection film for a second wavelength range of light which is different from the first wavelength range of light is lower than the reflectance of the first anti-reflection film for the second wavelength range of light.