Simulations of current-voltage (I-V) characteristics of Al/SiO2/Si MOS structures are carried out considering the effect of a spatial non-uniformity of the oxide film. The dispersion of the averaged (over the device area) current density is predicted dependent on the ratio between the gate dimensions and the characteristic length of thickness variations. Calculations rely on the new information on the tunneling parameters, which ensures the quantitative accuracy. Some experimental data, related to the oxide thickness statistics, are also discussed. (c) 2005 Elsevier Ltd. All rights reserved.