PURPOSE: To perform a stabilized oscillation with a high refractive index by a method wherein the form of an active layer is formed in a recessed state in such a way that the central part thereof becomes thinner than external members and the spreading of a P-N junction face between the active layer and a clad layer is made nearly equal.

CONSTITUTION: A clad layer 12 and an active layer 13 of a large thickness are grown on a substrate 11 by a liquid-phase epitaxial method. Then, a slit-shaped diffusion mask 17 is formed, an etching is performed in such a way that the thickness of the active layer 13 becomes 0.55∼1.4μm and the mask 17 is removed. Subsequently, a clad layer 14, a blocking layer 15 and a contact layer 16 are grown. Then, diffusion masks 18 are formed and a diffusion layer of a P type impurity concentration is formed up to 1.5μm in thickness. After that, a press-in diffusion is performed at 900°C and a P-N junction face 19 is formed. The diffusion masks 18 are removed, and positive electrodes 20 are formed on the layer 16, while a negative electrode 21 is formed on the lower surface of the substrate 11.