The electrical properties of semi‐insulating InP epitaxial layers grown by metalorganic chemical vapor deposition using CCl4as a doping source have been studied as a function of the growth conditions of the material. Secondary ion mass spectrometry has been used to analyze the incorporation of impurity species in these layers. These measurements indicate that the resistivities of the CCl4‐doped InP layers increase exponentially (exceeding 1012&OHgr; cm) with increasing growth temperature. The incorporation of C, H, and Cl decreases in these layers. In conjunction with the dependence of the resistivity on the flow rate of the diluted CCl4dopant during growth, these results suggest that the semi‐insulating nature of the InP layers is due to CCl4‐mediated incorporation of one or more defects during growth. It is not likely that either a deep level created by Cl or hydrogen passivation of shallow donors and acceptors is responsible for the electrical properties of this material. ©1995 American Institute of Physics.