There is increasing interest in the alpha polytype of Ga₂O₃ because of its even larger bandgap than the more studied beta polytype, but in common with the latter, there is no viable p-type doping technology. One option is to use p-type oxides to realize heterojunctions and NiO is one of the candidate oxides. The band alignment of sputtered NiO on α-Ga₂O₃ remains type II, staggered gap for annealing temperatures up to 600 °C, showing that this is a viable approach for hole injection in power electronic devices based on the alpha polytype of Ga₂O₃. The magnitude of both the conduction and valence band offsets increases with temperature up to 500 °C, but then is stable to 600 °C. For the as-deposited NiO/α-Ga₂O₃ heterojunction, ΔE_V = −2.8 and ΔE_C = 1.6 eV, while after 600 °C annealing the corresponding values are ΔE_V = −4.4 and ΔE_C = 3.02 eV. These values are 1−2 eV larger than for the NiO/β-Ga₂O₃ heterojunction.