Nitrogen (N) doping in ZnO is studied to realize reproducible p-type conductivity. Undoped ZnO layers prepared on a-face of sapphire substrates with H2O vapor-assisted growth showed n-type conductivity. However, N-doped ZnO (ZnO:N) layers grown in the similar manner showed the type conversion to p-type conductivity. As-grown p-type ZnO:N layers showed low net acceptor concentrations (NA–ND) of ~ 1014 cm-3, but thermal annealing of the N-doped ZnO samples as well as the optimization of growth parameters increased the NA–ND up to ~ 5×1016 cm-3. Photoluminescence measurements showed consistent spectra with the electrical properties by a clear conversion from neutral donor-bound exciton emission in n-ZnO to neutral acceptor-bound exciton emission in the p-ZnO layers.