The surface treatment method using chemical etching for Zn-polar zinc oxide (ZnO) single-crystal substrates without annealing is proposed. The wet-chemical etching of Zn-polar ZnO had a serious issue that led to the formation of a large number of etch pits at the surface together with the formation of step structure. After various experiments, the pH control of the solution during wet-etching at first stage of the etching is found to be very important to obtain the straight step-edges without formation of etch-pit. Atomically flat substrates without etch pits were able to be obtained by controlling the pH in BHF solution. Eventually, homoepitaxial ZnO thin films with atomically flat surface were formed as well. (C) 2010 Elsevier B.V. All rights reserved.