The pseudobinary III/V system GaAs1−ySbyis well known to have a solid phase miscibility gap with a critical temperature of 751 °C. We have succeeded in growing epitaxial layers of GaAs0.5Sb0.5lattice matched to InP at temperatures of 600 and 630 °C using the organometallic vapor phase epitaxy technique. The key requirement is a III/V ratio of greater than unity. This leads to the incorporation of all As and Sb reaching the interface and the ability to grow metastable alloys. The epitaxial GaAs0.5Sb0.5layers have excellent surface morphology and efficient photoluminescence at a wavelength of 1.6  &mgr;m.