A lattice-mismatched InP epitaxial layer on a GaAs(100) substrate was grown by the metal-organic chemical vapor deposition. Double-crystal X-ray diffraction was used to evaluate the crystallization and the crystal quality of the InP films. Transmission electron microscopy and Raman spectroscopy measurements showed that there was a lattice mismatch between the InP epitaxial layer and the GaAs substrate. The efficient photoluminescence measurements compared with those of InP homoepitaxy showed that high quality epitaxial films of InP could be grown on p-GaAs(100).