Analytical electron microscopy techniques are used to investigate elemental distributions across high-k dielectric stacks with metal gates. Electron energy-loss spectroscopy results from Si(100)/SiO2/HfO2/TiN and Si(100)/SiO2/HfO2/TiN/poly-Si gate stacks show evidence of interface reactions having occurred at the TiN/poly-Si interface and possibly at the HfO2/TiN interfaces. As interface reactions are likely to dominate the work function behavior of such systems, this technique offers unique capabilities to improve understanding of the work function behavior observed electrically. (c) 2006 The Electrochemical Society.