Breakdown characteristics of Hf-based high-k dielectrics in a wide thickness range were investigated to identify the "weak link" in the gate stack and its leading breakdown mechanisms under inversion stress. A strong correlation among the growth rates of the stress leakage current, SILC, and interface trap density suggests that breakdown is triggered by trap generation in the interfacial SiO2 layer. Stress-time evolution of the differential resistance and its slope obtained from SILC data allows progressive breakdown in high-k/metal gate stacks to be identified