Liquid phase epitaxy of Ga//xIn//1// minus //xP on (100-oriented GaAs and GaAs//0//. //8P//0//. //2 substrates has been studied. Results indicate that the solidus compositions of Ga//xIn//1// minus //xP both substrates tend to be ″locked near the lattice matching composition. This ″composition pulling effect is shown to be consistent with a model that takes account of the contribution of lattice mismatch strain energy.