PURPOSE: To obtain a ridge-type semiconductor laser device having stable characteristics by a method wherein an optical waveguide having high controllability is formed without etching of a cap layer and an upper cladding layer themselves.

CONSTITUTION: A stripe trench is formed in an n-type GaAs layer 14 on a p-type GaAs substrate 13 with high controllability of the trench width by photoelectrochemical selective etching (PEC). After the trench is filled with a p-type AlGaAs cladding layer 4 so as to have a flat surface, the p-type AlGaAs cladding layer 4 is further made to grow to have a required thickness to form an optical waveguide having high controllability.