A strong polarity effect on the temperature dependence of the leakage current in TiN/HfO2/SiO2/Si capacitors is reported. A model is proposed to explain these experimental results that combines tunneling through the stack and Frenkel–Poole hopping in the HfO2 layer, depending on the value of the gate voltage. It is shown that the polarity effect most probably results from the anisotropy of the band diagram of the HfO2/SiO2 stack, as well as from the location of the shallow traps with respect to the conduction band of the HfO2 layer. Comparison of the model with the experimental results allows an estimate of the trap depth to be between 0.5 and 0.8 eV. © 2002 American Institute of Physics.