Abstract: A distributed feedback semiconductor laser having a diffractive grating on an active layer in order to generate stimulated emission by recombing electrons with positive holes thereon by the light distributed feedback. This laser can achieve precisely single wavelength longitudinal mode lasing as a thin buffer layer is grown on the surface of the semiconductor layer which has been etched with irregular pattern corresponding to the diffractive grating while the corrugated pattern is being maintained intact and an active layer is grown on the surface thereof in a manner to fill in the valleys of the corrugated pattern as much as possible so that a diffractive grating is formed on the active layer and light distributed feedback is caused mainly by the periodic perturbation of gain coefficients stimulated by the diffractive grating.