Spatial distributions of electrically active defects in dual-layer (SiO2/HfO2) gate dielectric n-type metal oxide semiconductor transistors have been determined by charge pumping and 1/f low-frequency noise measurements. Oxide trap concentration levels extracted from both techniques are in good agreement and appear one decade greater for HfO2 oxides compared to the reference SiO2 one. Moreover an increase in the trap concentration at the SiO2/HfO2 is observed that could explain threshold voltage instabilities currently observed in HfO2 based transistors. (C) 2009 American Vacuum Society. [DOL 10.1116/1.3025824]