The device performance and reliability of nitride/oxide stack gate dielectrics with different buffer oxide thickness has been studied. The stack dielectrics were fabricated by in situ H(2%)/O-2 anneal of chemical vapor deposited Si3N4. Ellipsometry data indicates the formation of SiO2 at the Si3N4/Si interface. With decreasing thickness of the buffer oxide, the gate leakage current reduced while the reliability and metal oxide semiconductor field effect transistor performance were degraded. The degradation in the reliability is attributed to the extension of structural strained layer into the Si3N4 bulk. Our results suggest that a buffer oxide of similar to10 Angstrom is needed for the implementation of Si3N4 gate dielectric for future high performance complementary metal oxide semiconductor devices. (C) 2002 The Electrochemical Society.