The electron energy band alignment at the Si/HfO2 interfaces with different interlayers (Si3N4, SiON, and SiO2) is directly determined using internal photoemission of electrons and holes from Si into the Hf oxide. Irrespective of the interlayer type, the energy barrier for the Si valence electrons was found to be equal 3.1+/-0.1 eV, yielding the conduction band offset of 2.0+/-0.1 eV. Photoemission of holes is effectively suppressed by SiON and SiO2 interlayers, yet it is observed to occur across the Si3N4 interlayer with a barrier of 3.6+/-0.1 eV, which corresponds to a Si/HfO2 valence band offset of 2.5+/-0.1 eV. The HfO2 band gap width of 5.6 eV, thus derived from the band offsets, coincides with the bulk value obtained from the oxide photoconductivity spectra. (C) 2002 American Institute of Physics.