Electrical properties of epitaxial CeO2 thin films on silicon (111) substrates grown in ultrahigh vacuum were studied, varying growth conditions and ex situ thermal treatments. Characterization using reflection high‐energy electron diffraction and high resolution transmission electron microscopy reveal that while the ceramic layers have a good single‐crystal structure, a dual amorphous layer of CeOx and SiO2 forms at the CeO2/Si interface. This structure has undesirable electrical properties, however, utilizing a post‐anneal in dry oxygen, the α‐CeOx layer was removed and the SiO2 amorphous layer was made thicker. This newly developed structure benefits from the SiO2/Si interface, having Dit=6×1011 cm−2, and Qf=5×1011 cm−2. The structure exhibits a high capacitance due to the large dielectric constant of CeO2, has electrical properties comparable with those of other reported gate insulators on Si, and has an epitaxial oxide lattice matched to Si. © 1994 American Institute of Physics.