In this article, we determine the band alignment at the thermodynamically stable heterointerface between a ( 2 ¯ 01 )-oriented single-domain β-(In_0.072Ga_0.928)₂O₃ crystal and bulk c-plane sapphire, namely, (0001)-oriented α-Al₂O₃. The β-(In_0.072Ga_0.928)₂O₃ layer was deposited on the bulk sapphire crystal using pulsed laser deposition. The β-(In_0.072Ga_0.928)₂O₃ and α-Al₂O₃ valence and conduction band offsets (VBO and CBO, respectively) were found to be 0 ± 0.1 and 4.87 ± 0.1 eV, respectively. Accordingly, we identified a type-I α-Al₂O₃/β-(In_0.072Ga_0.928)₂O₃ heterojunction. X-ray diffraction measurements confirmed ( 2 ¯ 01 )-oriented single-domain β-(In_0.072Ga_0.928)₂O₃ high-quality films with in-plane rotations of every 120 ∘ , whereas Rutherford backscattering spectrometry was employed to verify the bulk composition. We employed high-resolution X-ray photoelectron spectroscopy to measure the core level binding energies of Al 2p and Ga 2p_3/2 with respect to the valence band maxima of the β-(In_0.072Ga_0.928)₂O₃ and α-Al₂O₃ layers, respectively. Then, we measured the energy separation between the Al 2p and Ga 2p_3/2 core levels at the interface of the heterojunction. β-(InGa)₂O₃ is a wide-bandgap semiconductor, while α-Al₂O₃ is a well-known dielectric. Together, they can be employed to fabricate reliable and efficient power electronic devices. We also combined high-resolution transmission electron microscopy, X-ray diffraction, and fast Fourier transform algorithms to characterize the dislocations at the interface.