In this talk, we first review the first BD and post BD statistics of high-k/SiO2 bilayer films (or high-K stacks) by delineating similarities and differences from SiO2 single-layer films. Then, we will discuss the recent progress on TDDB voltage and temperature dependence in a two-step model of species-release and reaction process. This model is found to be applicable to both SiO2 and high-K stacks (pFET inversion mode) and provide a sound physical picture for overall BD process. Finally, we will highlight the challenges in AC TDDB reliability, specifically related to nFET inversion mode of high-k stacks. © 2013 IEEE.