InP layers were grown by organometallic vapor phase epitaxy (OMVPE) at atmospheric pressure using trimethylindium (TMI) and tertiarybutylphosphine (TBP) as source gases. Specular surfaces were obtained at growth temperatures between 550°C and 600°C and at the V/III ratio of 79. Electrical and optical characterizations were carried out to elucidate the behavior of unintentionally doped impurities in the grown layers. All the epitaxial layers showed n-type conductivity. The highest electron Hall mobilities were 3800 cm2V-1s-1at 300 K and 12000 cm2V-1s-1at 77 K with the electron concentrations of 7.5×1015cm-3and 6.8×1015cm-3, respectively. Possible impurity sources were discussed. © 1990 IOP Publishing Ltd.