Leakage current distribution in ultrathin SiO2 film formed on (I 1 1) Si surface with step/terrace structures was investigated using atomic force microscopy with a conductive cantilever. Regions with higher leakage current of 1.0-nm-thick SiO2 were observed in line along the atomic steps. In a case of 1.4-nm-thick SiO2, even if a relationship between the leakage current distribution and the atomic step positions is not observed at the initial stage, the high voltage stress application makes the relationship clear. The atomic step edges have a great influence on their initial leakage and the reliability of the ultrathin oxide. (C)2002 Elsevier Science B.V. All rights reserved.