The origin of flat band voltage (V-FB) shift with La2O3 insertion for HfO2 gate dielectrics has been carefully examined. By separating the effect of the fixed charges located at each interface by thickness-dependent V-FB evolution, total voltage shifts (dipole) at metal/high-k and high-k/SiO2 interfaces have been estimated. Using stacked capacitors of La2O3 and HfO2, it can be concluded that V-FB is mainly determined by the high-k on SiO2. Therefore, the dipole at La2O3 and the interface has an additional dipole of 0.36 eV compared with that of HfO2/SiO2. The same trend has also been obtained with a high-k on a Si substrate without a SiO2 layer. A simple model using electronegativity has been proposed to explain the V-FB shift. (C) 2008 Elsevier Ltd. All rights reserved.