At least a lower cladding layer, an active layer for generating laser light, a first upper cladding layer, an etching stopper layer and a second upper cladding layer are stacked on a substrate. An impurity for restraining laser light absorption is diffused into the second upper cladding layer along a region where a light-emitting end surface is to be formed, under a condition that allows the etching stopper layer to maintain a function of stopping etching for the second upper cladding layer (First annealing process). Etching is performed until the etching stopper layer is reached such that the second upper cladding layer is left in a ridge shape. The impurity in the second upper cladding layer is re-diffused into the active layer to thereby cause local intermixing of the active layer in a portion extending along the light-emitting end surface and located just under the ridge (Second annealing process).