In this work, we present the reliability of HfO 2 and how it depends on the barrier height and the nature of the bi-layer structure. We will also discuss how these factors lead to different charge fluence, charge-to-breakdown, and breakdown characteristics. It is found that the lower Weibull slope of high-k dielectrics is partially attributed to high charge fluence by the lower barrier height of high-k dielectrics, and a different nature of bi-layer structure. In addition, it has been found that there is distinct bi-modal defect generation rate for high-k/SiO 2 stack. A two-step breakdown process was clearly observed. Soft breakdown characteristics were dependent on the barrier heights. It is attributed to different charge fluence by different barrier heights. Charge-to-breakdown shows strong barrier height dependence.