We have proposed a mechanism of nonideality in nearly ideal Au/n-Si Schottky barriers (SBs), which explains various experimental observations called the T-o anomaly. Because of the nature of the metal-induced gap states (MIGS), positively ionized defects induced by the process very close to the interface are considered to cause local lowering of the Schottky barrier height (SBH) due to filling-up of the MIGS. The formulation of the defect density is revised to be consistent with the experimental observations. There is a potential drop of more than 100 mV at about 20 Angstrom from the interface due to the space-charge of the defects. The saddle potential for the low-SBH spot is lowered by this potential drop. Therefore, the local SBH lowering is observable in the I-V characteristics. (C) 2003 Elsevier Science B.V. All rights reserved.