PURPOSE: To form an active layer of a multiplex quantum well without damaging the shape of a diffraction grating in a distributed feedback type semiconductor laser.

CONSTITUTION: On a P-InP substrate, the following are laminated in order by an organic metal vapor growth method; an N-InP buffer layer 32, an active layer 24 of a multiplex quantum well, a P-InGaAsP optical waveguide layer 34 and a P-InP buffer layer 26. After that, a diffraction grating 28 is formed in the buffer layer 26. Since the diffraction grating 28 is formed after the active layer 24 is laminated, the active layer 24 can be laminated by an organic metal vapor growth method, in the state that the shape of the diffraction grating 28 is not damaged by thermal decomposition. A P-InGaAsP optical waveguide layer 30 and a P-InP clad layer 36 are laminated in order on the diffraction grating 28 by liquid growth method. Since the buffer layer 26 and the optical waveguide layer 30 are composed of an InP layer and an InGaAsP layer, respectively, the buffer layer 26 is not subjected to melt-etching by InGaAsP solution for laminating the optical waveguide layer 30, and therefore the shape of the diffraction grating is not damaged.