The physical properties and charge trapping behavior of rapid thermal N2O-oxynitrided (RTON) and rapid thermal NH3-nitrided (RTN) ultrathin SiO2 films have been investigated. The results of secondary-ion-mass spectrometry and Fourier transform infrared reflection measurements indicate that although nitrogen atoms are incorporated into the RTON and RTN films, only the RTN film shows a large number of NH bonds in the bulk SiO2. Using an analytical model, the number of oxide charge traps, the capture cross section, and the charge trap generation rate for the RTON and RTN SiO2 films were determined. Under high-field stress, the RTON SiO2 film has a much smaller number of electron and hole traps and a lower electron trap generation rate, resulting in a larger charge-to-breakdown QBD value compared to that of pure SiO2 film. In contrast, a large number of electron traps which originate from NH and SiH bonds is present in the RTN film. The differences in the charge trapping phenomena and oxide breakdown characteristics are strongly related to the chemical bonding state in the bulk oxide. © 1997 American Institute of Physics.