We discuss the gate electrode effects on SiO2 degradation in MOS structures. The gate electrode material was poly‐silicon, but the impurity doping procedure was varied in terms of species and concentrations. First, the origin of the substrate hole current observed in n‐MOSFETs, by injecting electrons from the silicon substrate, is discussed in terms of oxide thickness and gate electrode doping species, because the dielectric breakdown is closely related to the total hole fluence in the oxide. The effects of the gate electrode on the oxide network structure and on the Si/SiO2 interface are also experimentally investigated. Finally, the experimental results obtained for Qbd of different gate electrode MOSFETs are shown, including the polarity dependence of Qbd. Furthermore, the percolation analysis to explain the polarity dependence is introduced, since the dielectric breakdown process is really stochastic.