A semiconductor optical device comprises a first conductive type semiconductor region, an active layer provided on the second semiconductor portion of the first conductive type semiconductor region, a second conductive type semiconductor region on the side and top of the active layer, the side of the second semiconductor portion, and the second region of the first semiconductor portion of the first conductive type semiconductor region, a potential adjusting semiconductor layer provided between the second semiconductor portion of the first conductive type semiconductor region and the active layer, and first and second distributed Bragg reflector portions between which the first conductive type semiconductor region, the active layer and the second conductive type semiconductor region is provided. Bandgap energies of the first conductive type semiconductor region and second conductive type semiconductor region are greater than that of the active layer. The second region of the first semiconductor portion of the first conductive type semiconductor region and the second conductive type semiconductor region constitute a pn junction. A bandgap energy of the potential adjusting semiconductor layer is different from bandgap energies of the first conductive type semiconductor region and the second conductive type semiconductor region.