PURPOSE: To obtain a diffraction grating consisting of a second semiconductor layer without dislocation by laminating the second semiconductor layer having meltback resistance larger than a first semiconductor layer onto the first semiconductor layer, forming fine irregularities to the second semiconductor layer while partially exposing the first semiconductor layer and melting back the exposed section of the first semiconductor layer.

CONSTITUTION: An active layer 4, a guide layer 3 as a first semiconductor layer and a P type InP layer 8 as a second semiconductor layer are all laminated onto an N type InP substrate 1 in approximately 0.1μm thickness, and a diffraction grating 2, which punches through the layer 8 and has a 2,400 period, is shaped to the layer 8 through etching, etc. A semiconductor having high meltback resistance is used as the layer 8 at that time, the surfaces of the layers 3 in sections exposed by the layer 8 are melted back, and slight meltbacks are also generated in the surface of the layer 8. Accordingly, a surface layer, on which residual fouling and a surface oxide adhere and which is thermally deteriorated, is removed, and a P type InP clad layer 5 is grown on the whole surface containing the diffraction grating 2 composed of the layer 8.