We investigated the distribution of tunneling current through ultrathin oxide films on Si(111) with an atomic force microscope (AFM) using a conductive tip. The oxides were grown in dry O-2 at 600 degrees C with or without post-oxidation annealing. For the oxide without post-oxidation annealing, we observed high tunneling current in the vicinity of step edges, which could be attributed to localized interface states around the step edges, while we could not detect such localized states for the oxides with post-oxidation annealing in H-2. This is an evidence that the localization states are active interface states and therefore, they were terminated with hydrogen during annealing. These results were supported by the conventional current-voltage (I-V) measurement on metal oxide semiconductor (MOS) capacitors with 1.5-nm-thick oxides, showing the larger current for the substrates with the higher step density. The tunneling current was drastically reduced after the post-oxidation annealing.