We provide direct and unambiguous experimental spectroscopic evidence for the structure of a switching oxide trap in thermally grown SiO2gate oxides on Si. Switching oxide traps can ‘‘switch’’ charge state in response to changes in the voltage applied to the gate of a metal‐oxide‐semiconductor field‐effect transistor. Electron spin resonance measurements reveal that someE&ggr;′centers (a hole trapped at an oxygen vacancy) can behave as switching oxide traps. ©1995 American Institute of Physics.