High-temperature cubic phase of HfO2 was observed by reflection high-energy electron diffraction in nanocrystalline thin films grown by atomic layer deposition from HfCl4 and H2O at substrate temperatures of 880-940 degreesC. The phase was formed at properly chosen precursor doses and it was observed on the surface of films, which according to X-ray diffraction data consisted of monoclinic HfO2. The thickness of the surface layer, in which the cubic phase appeared, was estimated to be 5-10 nm. According to Auger electron spectroscopy data, formation of the cubic phase was accompanied with an increase in the ionicity of O-Hf bonds.