The energy band offsets between indium-gallium-zinc oxide (IGZO) and β-Ga2O3 were examined by angle-resolved X-ray photoelectron spectroscopy (AR-XPS). The Ga 2p spectra from the heterojunction contributed by the upper IGZO film and the β-Ga2O3 substrate were deconvoluted into two sub-peaks with the binding energy difference of 0.3 eV, in good agreement with the theoretical model. Meanwhile, the bandgaps of IGZO and β-Ga2O3 were measured to be 3.44 ± 0.1 and 4.64 ± 0.1 eV from the ultraviolet-visible (UV-vis) transmittance spectra. The valence and conduction band offsets between the IGZO and β-Ga2O3 were consequently determined to be 0.49 ± 0.05 and 0.71 ± 0.1 eV, respectively. These findings reveal that IGZO is an attractive intermediate semiconductor layer (ISL) for reducing the electron barrier height at metal/Ga2O3 interfaces.