Abstract: A highly efficient light emitting semiconductor device which is stable at high speeds and has a low threshold current comprising a first semiconductor layer of a first conductive type; a second semiconductor layer of the second conductive type which is different from the first conductive type; an active layer composed of laminated semiconductor layers of the quantum well structure interposed between the first and second semiconductor layers and having a narrower effective energy band gap than the first and second semiconductor layers and a diffraction grading formed in either one of the first or second semiconductor layers.