In a monolithic dual-laser semiconductor laser device capable of high power output, a window structure for each of laser elements is formed through a common step, thereby improving the device reliability. The semiconductor laser device has an infrared laser element li0 and a red laser element 120 monolithically integrated on an n-type semiconductor substrate i01. Each of the infrared and red laser elements 110 and 120 has a ridged waveguide and a window structure formed by Zn diffusion at each resonator facet. The infrared and red laser elements ii0 and 120 include p-type contact layers 109 and 119 on the ridges of the respective waveguides. The p-type contact layer 109 is thinner than the p-type contact layer 119.