We report vertically aligned ZnO nanostructures grown using periodically polarity-inverted (PPI) ZnO heterostructures on (0001) Al2O 3 without the aid of a catalyst. In order to fabricate the PPI ZnO templates, the polarity control of ZnO film via in situ crystal polarity control methods using CrN and Cr2O3 buffer layers was used. Vertically aligned ZnO nanowires or nanowalls were formed only on the Zn-polar regions. The self-catalyzed process on the Zn-polar surface was most likely responsible for this selective growth. Finally, we determined the mechanism of nanowall formation on the basis of the coalescence of several nanowires in the defined area.