Single-crystal growth of GaP on the (111) face of a silicon substrate has been achieved at atmospheric pressure by the thermal decomposition of a gas-phase mixture of gallium triethyl and phosphorus triethyl at 485 C. A word of caution is included on the reactivity and toxicity of these organometallic compounds. Present work on the growth of thicker films and the electric characterization of the resulting heterojunctions is to be reported at a later date.