According to an aspect of the present invention, there is provided a method for assembling a semiconductor laser device, including: preparing a laser chip including: a substrate; stripe waveguides that are formed on the substrate and that each includes a gain producing area and a window area; electrodes formed on the stripe waveguides; an insulating layer formed on the electrodes; a metal layer formed on the insulating layer; projections arranged at an interval in the window areas; and joining structures connected to the electrodes and formed in the window areas; preparing a submount including: a first solder; second solders arranged at the interval; and submount electrodes connected to the second solders; contacting the laser chip to the submount by fitting the projections with respect to the second solders; and heating the submount and the laser chip.