The family of spinel compounds is a large and important class of multifunctional materials of general formulation ABX with many advanced applications in energy and optoelectronic areas such as fuel cells, batteries, catalysis, photonics, spintronics, and thermoelectricity. In this work, it is demonstrated that the ternary ultrawide-band-gap (∼5 eV) spinel zinc gallate (ZnGaO) arguably is the native p-type ternary oxide semiconductor with the largest E value (in comparison with the recently discovered binary p-type monoclinic β-GaO oxide). For nominally undoped ZnGaO the high-temperature Hall effect hole concentration was determined to be as large as p = 2 × 10 cm, while hole mobilities were found to be μ = 7-10 cm/(V s) (in the 680-850 K temperature range). An acceptor-like small Fermi level was further corroborated by X-ray spectroscopy and by density functional theory calculations. Our findings, as an important step toward p-type doping, opens up further perspectives for ultrawide-band-gap bipolar spinel electronics and further promotes ultrawide-band-gap ternary oxides such as ZnGaO to the forefront of the quest of the next generation of semiconductor materials for more efficient energy optoelectronics and power electronics.