Heteroepitaxy of a highly mismatched system (∼8%), InP/Si, has been studied using low‐pressure organometallic vapor phase epitaxy. GaAs buffer layer effects on residual stress and defect density in InP/Si have been clarified. Using a 1‐&mgr;m‐thick GaAs buffer layer, residual stress in the InP layer has been reduced to as low as 2×108dyn/cm2compared to ∼4×108dyn/cm2for InP directly grown on Si. Moreover, the GaAs buffer layer has also been confirmed to be effective for improving InP/Si quality by evaluation of etch‐pit density, x‐ray diffraction measurement, and cross‐sectional transmission electron microscopy. Electrical properties of InP layers on GaAs/Si were evaluated with the van der Pauw and deep level transient spectroscopy (DLTS) methods. The heteroepitaxial layer’s own electron trap has also been observed by DLTS measurements. For an InP/GaAs/Si structure, InP growth temperature effect on surface morphology and etch‐pit density is also shown. High quality InP films with an etch‐pit density of 8×106cm−2have been obtained on Si substrates by using thermal cycle growth and InP/GaAs/Si structure.