Oxide breakdown in metal-oxide-semiconductor (MOS) devices in the nanometer scale is simulated as a cluster growth depending process in which the local electric field is a function of a randomly varying local dielectric permissivity. Effects of MOS device bias polarity, film thickness and non-uniform defect distributions through the entire oxide film on the breakdown are studied. The slope of the Weibull distribution increases with the oxide thickness in agreement with experimental results. (C) 2002 Elsevier Science B.V. All rights reserved.