Double-heterostructure (DH) diode lasers based upon very thin epitaxial layers of Ga.sub.x In.sub.1-x As.sub.y P.sub.1-y grown on and lattice-matched to oriented InP substrates are disclosed. A preferred method for fabricating such lasers involves the successive growth, on an InP substrate, of an InP buffer layer, the GaInAsP active layer and an InP top barrier layer using liquid phase epitaxy techniques to grow these layers from supercooled solutions. Stripe geometry lasers can be fabricated from these materials which emit in the 1.1-1.3 .mu.m range and are capable of cw operation for extended periods at room temperature.