The method applies to manufacture of a semiconductor laser device which comprises a semiconductor substrate and a plurality of semiconductor layers piled sequentially one on top of another on the semiconductor substrate, the semiconductor layers including at least a first clad layer; an active layer interposed between a pair of optical waveguide layers, and a second clad layer. In the present manufacturing method, a first impurity diffusion source film is applied on top of the semiconductor layers, an insulation film is applied on top of the first impurity diffusion source film, two layers consisting of the first impurity diffusion source film and insulation film are removed respectively into a stripe shape except for the areas of the semiconductor layers in which impurities are to be diffused, a diffusion protect film to be etched selectively with respect to the insulation film is formed on the surfaces of the semiconductor layers and two layers, an impurity is thermally diffused from the first impurity diffusion source film, a diffusion protect film is etched selectively with respect to the insulation film, and a second impurity is diffused with the insulation film as a mask.