We report the synthesis of high quality single crystalline ZnO nanowall networks (NNs) using ammonia solution etching of a ZnO nanowire-nanowall heterojunction (NNH) structure. Synchrotron X-ray diffraction revealed that the full-width-at-half-maximum of the ZnO (0002) peak in the ZnO NN sample was much narrower than that of the ZnO NNH sample. Temperature-dependent photoluminescence (PL) measurements revealed more intense and narrower bound exciton peak emission in the NN sample compared to that in the NNH sample. Moreover, the clear observation of free exciton emission in the PL spectrum of the NN sample, even at temperatures as low as 30 K, suggested incorporation of a small number of impurities into the NN sample. In addition, I-V characteristics confirm the higher conductivity of the ZnO NNs as compared to those of the NNH structures, indicating that the NN sample had a superior crystalline property than NNH sample.