The growth of InP layers on GaAs substrates by molecular bi am epitaxy (MBE) using gallium phosphide (GaP) as a phosphorus sourer was investigated. The surface reconstruction during the growth was monitored by reflection high energy electron diffraction (RHEED), the high-quality InP layers on GaAs substrates with specular surface morphology could be obtained. The effects of growth temperatures and V/III ratios on the properties of InP epi-layers were studied. The undoped layers showed n-type conduction behavior with a background carrier concentration of 4 x 10(16)- 9.5 x 10(18) cm(-3) and mobility of 237-1761 cm(2)V(-1)s(-1), both at room temperature, as measured by van der Pauw method. Our results showed a strong dependence of growth quality on growth conditions such as growth temperatures and P-2/In flux ratios.