A semiconductor optical device

PROBLEM TO BE SOLVED: To provide a monolith-integrated semiconductor optical element formed of a group IV semiconductor capable of causing a light-emitting element to emit light at high efficiency and allowing a light receiving element to receive light at high efficiency.SOLUTION: The semiconductor optical element is formed of single crystal silicon subjected to doping, which includes an electrode; a light-emitting layer; and a light-receiving layer formed on an insulator film. A thin-line waveguide is formed between the light-emitting layer and the light-receiving layer. A stressor formed of silicon nitride having a compression strain is formed to cover the light-receiving layer. A stressor formed of silicon nitride having an extension distortion is formed to cover the light-emitting layer. The band gap/energy of the light-receiving layer is set to be smaller than the band gap/energy of the light-emitting layer.