Heteroepitaxial CdS films (60 nm) have been deposited at $\rm 85\ ^\circ C$ on GaP from aqueous solutions of ammonia containing cadmium ions and thiourea precursors. Structural characterizations have been performed with RHEED, five circle XRD and TEM observations of cross sections. The large lattice mismatch results in the formation of a large density of stacking faults in the CdS leading to a polytype structure with an equal proportion of cubic and hexagonal modifications. Changes in the lattice parameter are observed in the CdS near the interface.