A semiconductor light-emitting device fabricated as a double hetero-structure InGaAsP/InP-type laser. The laser includes a buffer layer made of a semiconductor. The buffer layer is located at the upper edge of the flow region of electrons as seen from the active layer. The conductivity type of the buffer layer is opposite to that of a clad layer located at the upper edge of the flow region of electrons seen from the buffer layer. A, the band gap of the buffer layer is wider than that of the active layer but narrower than that of a clad layer adjacent to the buffer layer. The thickness of the buffer layer does not exceed the diffusion length of the electrons injected into the buffer layer.