We report the epitaxial growth of silicon on a CaF2/Si(111) heteroepitaxial structure. The results show that contrary to previous reports, the room‐temperature predeposition of a very thin layer of silicon does not significantly affect the problem of calcium migration to the top surface of the silicon film, although it appears to improve the surface morphology of the film. Planar and cross‐sectional transmission electron microscope and x‐ray diffraction studies have shown that the silicon film, although single crystalline, is highly defective, the main defects being twins on both the inclined {1¯11} planes and the parallel (111) planes.