X -Ray Photoelectron Spectroscopy was used to determine the valence band offset at Al2O3/beta-Ga2O3 heterointerfaces. The Al2O3 was deposited either by Atomic Layer Deposition (ALD) or rf magnetron sputtering and the synthesis method was found to have a very significant effect on the resulting band alignment. The bandgaps of the materials were determined by Reflection Electron Energy Loss Spectroscopy as 4.6 eV for Ga2O3 and 6.9eV for Al2O3 deposited by either method. The valence band offset was determined to be 0.07eV 0.20 eV (straddling gap, type I alignment) for ALD Al2O3 on Ga2O3 and -0.86 0.25 eV (staggered gap, type II alignment) for sputtered Al2O3. This led to conduction band offsets of 2.23 0.60 eV for ALD Al2O3 and 3.16 0.80 eV for sputtered Al2O3, respectively. The choice of deposition method for the dielectric alters the type of band alignment for the Al2O3/Ga2O3 system from type I alignment to type II. Since the main difference is expected to be the disorder at the dielectric/Ga2O3 interface, this shows how synthesis method can affect the resulting band alignment. (C) 2017 Elsevier Ltd. All rights reserved.