The high partial pressure of phosphorus at the stoichiometric melting point of InP precludes the in-situ synthesis in the puller by simple admixture of indium and phosphorus. This paper describes a system that was considered for the in-situ synthesis and growth of InP single crystal, utilizing the phosphorus vapor injection method. The advantages of this two-heater side-by-side injection synthesis system is dis-cussed and the effect of chamber pressure and phosphorus temperature on the InP synthesis yield is described. The procedures used for in-situ synthesis and growth are also described. Electrical and optical properties of LEC cry-stals grown by in-situ synthesis compare favorably with those of crystals grown from polycrystalline charges synthe-sized with the high-pressure autoclave or the gradient freeze method.