The breakdown dynamics of ultrathin SiO2 films in metal-oxide-semiconductor structures has been investigated. We show that the progressive increase of the leakage current that flows through the oxide when subjected to constant electrical stress can be modeled by the stochastic logistic differential equation. This approach relies on a time scale separation in which a deterministic term provides the S-shaped growth trajectory while a second term of the equation deals with the noisy behavior. Because of the inherent mean reverting property of the simulation process, the proposed model is also able to cover cases in which sudden upward and downward changes of the system's conductance are registered. (C) 2003 American Institute of Physics.