After scrutiny of the common stable defects in ZnO, two possible origins for the defect peak are proposed. One is Oi in bulk, which leads to a max. CLS of 1. Considering the crucial role played by native defects in metal oxide semiconductors, misinterpretation of XPS results may lead to wrong conclusions when trying to correlate defects with certain mechanisms or properties, which, in turn, would further misguide researches. This work aims to provide a reliable basis for defect analysis by XPS.