High performance NiO/β-GaO heterojunction pn diodes were realized by applying a sputtered p-type NiO film onto a lightly doped n-type β-GaO epitaxial layer. Taking advantage of the high barrier height against carriers within the pn heterojunction, the demonstrated device exhibited a high breakdown voltage (V)} of 1059 V without optimized electric field management techniques, and before breakdown the reverse leakage current density remained below 1μA/cm. Simultaneously, a relatively low specific on-resistance (R) of 3.5 mΩ· cm was achieved. The built-in potential of the heterojunction that determined by a capacitance-voltage (C-V) measurement was around 2.4 eV. As discussed in terms of the energy band diagram of a type-II heterojunction, the conduction band and valence band offsets at the NiO/β-GaO hetero-interface were estimated to be 1.2 and 2.3 eV, respectively.