CaF2films were deposited onto (100) cleavage faces of NaCl in a high‐vacuum bell‐jar system. The dependence of structure on substrate temperature and film thickness was studied by transmission electron microscopy and diffraction. When the substrate temperature was around 350°C during deposition, a simple(100)CaF2&bigsl;&bigsl;(100)NaClwith⟨110⟩CaF2&bigsl;&bigsl;⟨100⟩NaClepitaxial monocrystalline orientation was found. Complex(110)CaF2&bigsl;&bigsl;(100)NaClwith average⟨111⟩CaF2&bigsl;&bigsl;⟨100⟩NaClepitaxial polycrystalline orientations were found when the substrate was in the 150°–250°C range during deposition. Hard‐sphere models of the CaF2and NaCl faces were used to interpret these results qualitatively.