The etching of zinc oxide (ZnO) thin films has been studied using a high density plasma in a Cl2/Ar gas. The etch characteristics of ZnO thin films were systematically investigated on varying Cl2 concentration, coil rf power, dc-bias voltage, and gas pressure. With increasing Cl2 concentration, the etch rate of ZnO thin film increased, the redeposition around the etched patterns decreased but the sidewall slope of the etched patterns slanted. As the coil rf power and dc-bias voltage increased, the etch rates of ZnO thin films increased and etch profiles of ZnO thin films were improved. With increasing gas pressure, the etch rate of ZnO thin films slightly increased but little change in etch profile was observed. Based on these results, the optimal etching conditions of ZnO thin film were selected. Finally, the etching of ZnO thin films with a high degree of anisotropy of approximately 75°∼80° without the redepositions and residues was successfully achieved at the etching conditions of 20% Cl2 concentration, coil rf power of 1000 W, dc-bias voltage of 400 V, and gas pressure of 5 mTorr.