In this work we investigate the low frequency current noise in metal-oxide-semiconductor structures biased with a constant voltage in different oxide degradation stages. We report 1/f noise in fresh oxides with an anomalous current dependence that is quite similar to what has been reported in the direct tunneling regime. A higher flicker noise level is observed after stressing the oxide. Both observations are ascribed to the presence of an additional tunneling component assisted by native or stress-induced oxide traps. A further increase of the low frequency current noise is observed after the oxide breakdown (BD). It is shown that in the quantum point contact case single fluctuators, probably consisting of electron traps inside the oxide, can be resolved, whereas the current noise at the thermal BD presents a 1/f spectrum, due to the effects of ensemble averaging between many of these fluctuators. (C) 2002 Elsevier Science Ltd. All rights reserved.