Nitrided thermal oxide was used to reduce the degradation of top and bottom gate-insulators of self-aligned double gate metal-oxide-semiconductor field effect transistors that use a form: of selective epitaxial growth of silicon (SEG) called tunnel epitaxy. The degradation of thermal oxide was due to the exposure of gate insulator to the epi-growth ambient gases during the epitaxial growth. Both thermal oxide and thermally nitrided oxide samples were exposed to the epi-reactor gases and then the electrical characteristics were measured. Nitrided oxide showed significantly higher breakdown field, lower leakage current, and lower interface states than the thermal oxide after exposure to the selective epi-growth environment. For a 30 min stress in epi-reactor ambient, thermal oxide showed-average breakdown fields of less than 1 MV/cm due to the formation of pinholes, while nitrided oxide samples showed average breakdown fields of 15.6 MV/cm for same stress condition, interface state density (D (it)) of nitrided oxide improved after exposure to epitaxial growth ambient. The average D-it reduced from similar to3.5X 10(10)/cm(2) eV to similar to1.5X 10(10)cm(2) eV for a 30 min SEG/epitaxial lateral overgrowth stress. for nitrided oxides.