Two distinct peaks in the interface trap distribution on (100) Si, one above and the other below the Si midgap energy, have been observed in a wide selection of metal/SiO2/Si capacitors after they are exposed to ionizing radiation. The samples tested cover a wide range of gate electrode materials (Al, polycrystalline Si, Mo, and TiSi2) and oxidation environments [dry O2, steam, dry O2+TCA (trichloroethane), and dry O2+HCl at various temperatures]. Among all the samples tested, the peak above midgap (∼Ev+0.75 eV) appeared immediately after irradiation, and for most samples the peak below midgap (∼Ev+0.35 eV) only appeared at long times (up to a few months) after irradiation. The evolution of the two peaks as a function of time has been found to depend strongly on the gate electrode, oxidation environment, sample storage temperature, and gate bias during storage. Detailed studies of these two peaks should lead to a better understanding of the defect formation process at the SiO2/Si interface.