This work studies the constant current stressing effects on the ultrathin (1.7-3 nm) oxides prepared by thermal oxidation of silicon in nitric oxide (N2O). A simple process evaluation formula for extracting the stress-induced flatband shift is developed and validated with capacitance-voltage measurements. We find that the flatband degradation does not follow the power law, rather an exponential law with a quasi-saturation region is observed as a result of the slow trap generation rate or the generation of positive charge during the constant current stressing. The sources of trap generation are attributed to the Si-Si bonds, P-b centers, and nitride-related defects due to the over-constrained silicon atoms in the Si3N4 clusters at the interface. (c) 2005 Elsevier Ltd. All rights reserved.