MOVPE growth studies of GaAs(1-x)P(x) (x = 0.05-0.40) on GaAs substrates, combined with X-ray diffraction analysis and secondary-ion mass spectroscopy, have demonstrated a "compositional latching" effect in thin layer growth, where the incorporation of P from vapor to solid is suppressed due to lattice strain on the growing surface. A tentative growth model based on strain-dependent incorporation probabilities for P and As has been proposed. The grown surface feature is strongly dependent on the degree of relaxation of the lattice strain.