A first and second semiconductor laser, which comprise buffer layers, cladding layers, quantum well active layers, and cladding layers integrated on the substrate and have a stripe geometry, are integrated on a common substrate, with the quantum well active layers in the vicinity of the cavity facets disordered by impurity diffusion. Relationships .lamda.1>.lamda.b1, .lamda.2>.lamda.b2, .lamda.1>.lamda.2, and E1.ltoreq.E2 are satisfied, where .lamda.1 and .lamda.2 are defined, respectively, as the emission wavelengths of the active layers of the first and second semiconductor lasers, E1 and E2, respectively, as the forbidden band energies of the buffer layers of the first and second semiconductor lasers, and .lamda.b1 and .lamda.b2 respectively as the wavelengths corresponding to the forbidden band energies of the buffer layers of the first and second semiconductor lasers. The generation of reactive currents flowing through the window portions, which is caused by the intensification of disordering performed for window region formation, can be appropriately suppressed for both types of integrated semiconductor lasers.