We report an analysis of the heteroepitaxial interfaces in high quality GaInP-GaAs superlattices grown simultaneously on GaAs and Si substrates by gas source molecular beam epitaxy. These two superlattices have been studied using high resolution x-ray diffraction measurements. Sharp superlattice satellites, with very little broadening, are observed within a 6-degrees range for the sample on GaAs. Photoluminescence peaks with full widths at half-maximums of 5 and 7 meV are obtained at 4 K for samples with 58 angstrom wells on GaAs and Si, respectively. Room temperature exciton absorption is observed in the photovoltage measurements for a superlattice grown on Si substrate. The thicknesses determined by x-ray analysis are consistent with those obtained by a Kronig-Penny model fitting of the photovoltage spectroscopy.