A model for the leakage current of silicon oxide-silicon nitride-silicon oxide (ONO) dielectrics at low electric fields (≅2 MV/cm) was successfully developed. It is proposed that two transition mechanisms occur simultaneously. One is the detrapping of electrons from the silicon dangling bond in amorphous silicon nitride (SiN), which corresponds with the transition of dangling bonds among three possible charge states. The second is the direct tunneling of the detrapped electrons from the SiN to the gate through the thin silicon oxide. Both the location and the energy levels of the defect state are taken into account. The energy level, and the intrinsic time constant of the Si dangling bond and the uniform trap density in SiN, can be obtained by comparing the experimental results of the ONO discharge current with the calculated ones based on the above model. It can be found that the energy levels for negatively charged and neutral Si dangling bonds (E - and E 0 ), with respect to the SiN conduction band, are 1.2 and 2.0 eV, respectively, the intrinsic time constants t - and t 0 are 1.0×10 -14 and 4.0×10 -13 s, respectively, and the uniform trap density is 4.0×10 19 /cm 3 . From the energy level difference between E - and E 0 , we can conclude that the effective correlation energy of the Si dangling bonds in SiN is 0.8 eV, which is consistent with Robertson's results based on a tight binding calculation.