We report a novel fabrication method of spindle-like gallium oxide (Ga2O3) nanocrystals via two steps processed by electrochemical reaction of the MOVPE-grown GaN epitaxial layer in HF/ethanol (1:6) electrolyte and subsequent heat treatment. Depending on the electrolyte concentration, reaction time and applied voltage, micrometer- to nanometer-size spindle-like gallium fluoride tri-hydrate (GaF3 center dot 3H(2)O) of different densities and geometrical dimensions were formed on the surface of GaN. EDS, XPS and XRD were used to characterize the properties of the material before and after heat treatment. It is found that due to heat treatment at above 600 degrees C, nanocrystalline Ga2O3 were transformed from the GaF3 center dot 3H(2)O via pyrohydrolysis reaction mechanism. The band gap of similar to 5.1 eV of the spindle-like Ga2O3 was measured by the optical absorption spectroscopy. (C) 2016 Published by Elsevier B.V.