The dielectric strength of the gate oxide under a molybdenum polycide electrode (MoSi2 on polycrystalline silicon films) has been studied as a function of the fabrication processing steps of complementary metal oxide semiconductor very large scale integration. It was found that the thermal oxidation process step, after the source/drain formation using high dose BF2 ion implantation, thins the underlying polycrystalline silicon (poly-Si) of Mo polycide films and increases the degradation of thin gate SiO2 films in metal-on-oxide semiconductor capacitors. The effect of ion implantation on the oxidation behavior of Mo polycide films was compared with that of poly-Si films doped with phosphorus using a POCl3 source. An anomalous oxidation enhancement of Mo polycide films was observed when BF2 ions or BF2 and As ions are implanted into the Mo polycide films. This anomalous oxidation can cause gate oxide degradation.