High-resolution X-ray diffraction (HRXRD) was used to characterize linearly graded metamorphic InGaP buffer layers grown at different temperatures on GaAs substrate by solid-source molecular beam epitaxy. The sample grown at 380°C did not exhibit a Bragg diffraction peak corresponding to the top layers consisting of an InGaAs/InP single quantum-well structure, since it could not maintain a two-dimensional growth. When the samples were grown at higher temperatures (430–480°C), the top epitaxial layers were nearly fully relaxed and the strain relaxation anisotropy in two 〈110〉 directions was found to be small. It was also found that the growth temperature of the buffer layer for these samples did not influence the strain relaxation ratio. Moreover, the full width at half maximum (FWHM) values of the XRD peaks suggest that the sample grown at 480°C has better material quality.