An optical semiconductor device comprising: a semiconductor multilayer structure including an active region interposed between a first facet on a laser light emitting side and a second facet opposing to the first facet, and a first continuous electrode layer provided on a top of the semiconductor multilayer structure and a second continuous electrode layer provided on a bottom of the semiconductor multilayer structure; and an electrical connection region (24;33) 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, wherein α > β and β > 0 are satisfied, where of a total contact area between the electrical connection region and a top area of a selected one of the first electrode layer and the second electrode layer of the optical semiconductor device, the part of the contact area included in a half region on the first facet side of said top area of said selected one of the first electrode layer and the second electrode layer of the optical semiconductor device is denoted as α, and the part of the contact area included in a half region on the second facet side of said top area is denoted as β, and both a and β are contact areas connected to said top area of said selected one of the first electrode layer and the second electrode layer, wherein a part of the electrical connection region connected to the half region on the second facet side of said top area of the optical semiconductor device is located near the second facet, and wherein the electrical connection region is arranged and connected such that a current density distribution in a direction connecting the first facet and the second facet inside the active region is close to a photon density distribution in the same direction inside the active region. a semiconductor multilayer structure including an active region interposed between a first facet on a laser light emitting side and a second facet opposing to the first facet, and a first continuous electrode layer provided on a top of the semiconductor multilayer structure and a second continuous electrode layer provided on a bottom of the semiconductor multilayer structure; and an electrical connection region (24;33) 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, wherein α > β and β > 0 are satisfied, where of a total contact area between the electrical connection region and a top area of a selected one of the first electrode layer and the second electrode layer of the optical semiconductor device, the part of the contact area included in a half region on the first facet side of said top area of said selected one of the first electrode layer and the second electrode layer of the optical semiconductor device is denoted as α, and the part of the contact area included in a half region on the second facet side of said top area is denoted as β, and both a and β are contact areas connected to said top area of said selected one of the first electrode layer and the second electrode layer, wherein a part of the electrical connection region connected to the half region on the second facet side of said top area of the optical semiconductor device is located near the second facet, and wherein the electrical connection region is arranged and connected such that a current density distribution in a direction connecting the first facet and the second facet inside the active region is close to a photon density distribution in the same direction inside the active region.