Implantation of Si in does of 1015–1016cm−2into dry thermal oxides on silicon wafers produces a three‐state MOS memory device. For both positive‐ and negative‐going traps, gate voltage stress up to ±10 MV/cm−1generates stable (±) oxide charge near the gate and (∓) charge near the substrate. Electron paramagnetic resonance (EPR) measurement on corona‐field (≤11 MV/cm) stressed oxides revealsE’centers in regions of positive charge, which may be recycled between the EPR‐visible (+) state and the invisible neutral state. The correspondence of charge and EPR indicates a composite or Feigl‐Fowloer‐YipE’center, O33/4 Si:...+Si 3/4 O3, arising from nonstoichiometric Si fused into the SiO2lattice. Upon trapping an electron, the center rebonds to yield O33/4 SiSi 3/4 O3. The charging parameters of theE’center suggest tunneling of an electron from the (0→+) state, and are consistent with the theoretical prediction of the energy level and Franck–Condon relaxation. The three types ofE’centers observed in this and related studies are compared with theE’&agr;,E&bgr;andE’&ggr;variants of bulk amorphous silica.