An optical semiconductor device includes a semiconductor multilayer structure, an active region interposed between a first facet on a light emitting side and a second facet opposing to the first facet, and a first electrode layer provided on a top of the semiconductor multilayer structure and a second electrode layer provided on a bottom of the semiconductor multilayer structure; and an electrical connection region connected to at least one of the first electrode layer and the second electrode layer of the optical semiconductor device and used for injecting a current to the active region, and α>β and β>0 are satisfied where α is the contact area included in a half region on the first facet side in a top area of the optical semiconductor device and β is the contact area included in a half region on the second facet side.