Ga doped n-type ZnO layers are grown using plasma assisted chemical vapor deposition on Mg doped p-type AlGaN epitaxial layers grown by hydride vapor phase epitaxy to form n-ZnO/p-AlGaN heterojunction light emitting diodes. I-V characteristics clearly show rectifying behavior with a threshold voltage of ∼3.2 V and intense ultraviolet electroluminescence with peak emission at 390 nm. The dominant emission mechanism is found to result from hole injection from the p-type AlGaN into the n-type ZnO. Significant emission up to 500 K is observed indicating possible applications in harsh environments.