We have investigated the dynamics of hard intrinsic dielectric breakdown of gate oxide layers with thickness between 35 and 5.6 nm in n+ polycrystalline Si–SiO2–Si metal/oxide/semiconductor capacitors after constant voltage Fowler–Nordheim stress. The buildup of defects in the oxide during the degradation phase was monitored by quasi static C–V measurements. The dynamics of the final breakdown event was followed with high time resolution, allowing to measure voltage, current, and power versus time during the breakdown transient. Transmission electron microscopy data quantifying the damage produced during this transient are reported. Finally, we propose a phenomenological model concerning the dynamics of breakdown with model parameters adjusted on the basis of the experimental data. © 1999 American Institute of Physics.