Well-aligned ZnO nanowires (NWs) with tunable n-type conductivity are synthesized by introducing Ga2O3 as a dopant source in thermal evaporation. The crystallographic orientation of the NWs depends on the dopant content. Electrical transport property measurements on single nanowires verify that the resistivity of ZnO NWs can be controlled, with high reproducibility, by the Ga impurities.