Provided is a method of manufacturing a semiconductor device, which is adapted to prevent the deposition of a material on a laser light emitting edge, thereby enabling an improvement in longevity characteristics of a laser. A base having a laser chip mounted thereon is irradiated with an energy beam having a shorter wavelength than an oscillation wavelength of the laser chip. Photolysis and oxidation caused by the energy beam cause the removal of an adherent from the overall base or the deterioration thereof, and incidentally, the adherent is derived from an adhesive sheet used to attach the laser chip to the base, or the like. Preferably, laser light or ultraviolet light, for example, is used as the energy beam. Alternatively, the base having the laser chip mounted thereon may be irradiated with plasma so as to remove the adherent utilizing an ion cleaning effect of the plasma. After irradiation, a top is mounted to the base so as to shut off the laser chip from the outside.