A phase-locked laser array comprising a plurality of element regions for passing electric current into an active layer; and inter-element regions formed between the element regions. Each of the inter-element regions is so formed as to have two regions, i.e. a non-diffusion region at the center thereof and a diffusion regions disposed on both sides thereof, thereby rendering the refractive index in the non-diffusion region higher than that in the diffusion regions. The method of manufacturing the phase-locked laser array which is characterized by including a step growing an optical waveguide layer of superlattice on a portion of a second clad layer while diffusing impurities doped in the second clad layer into said optical waveguide layer, thereby forming a diffusion regions on both sides of the inter-element region.