A SONOS flash memory device, including a semiconductor substrate; an ONO structure formed on the semiconductor substrate, the ONO structure including a bottom oxide layer, a dielectric charge storage layer and a top oxide layer, the bottom oxide layer having a super-stoichiometric oxygen content and an oxygen vacancy content of about 10¹⁰/cm² or less, wherein the bottom oxide layer exhibits a reduced charge leakage relative to a bottom oxide layer having a stoichiometric or sub-stoichiometric oxygen content and a greater number of oxygen vacancies. In one embodiment, the bottom oxide layer has an oxygen vacancy content of substantially zero.