From the procedure developed for computing the In-Ga-P ternary phase diagram the InP-GaP pseudobinary phase diagram is generated. The free energies for the ternary liquid and pseudobinary solid are calculated as a function of composition, which establishes the stability of the solid us. the liquid and shows on what substrate liquid-phase epitaxial growth is possible. The composition variation of an InxGa1-xP solid that is deposited during cooling in liquid phase epitaxial growth under various conditions is calculated. © 1971, The Electrochemical Society, Inc. All rights reserved.