High quality Y2O3 on GaSb was achieved using both molecular beam epitaxy (MBE) and atomic layer deposition (ALD) with interfacial characteristics studied by in-situ X-ray photoelectron spectroscopy (XPS) and metal-oxide-semiconductor (MOS) electrical measurements. Ga-oxide and stoichiometric Sb-oxides were obtained in the MBE-Y2O3/GaSb and non-stoichiometric Sb(2)Ox (x<4) was found in the ALD-Y2O3/GaSb according to the XPS spectra. From the capacitance-voltage (CV) measurements, MBE-Y2O3 provides lower interfacial trap density (D-it) grown at elevated temperature of 200 degrees C, while ALD-grown Y2O3 shows smaller hysteresis and higher dielectric constant. (C) 2017 Elsevier B.V. All rights reserved.