TiN as gate electrode in Si/HfO2/TiN/poly-Si stack is evaluated after the postmetal annealing treatments. Interface reactions are investigated using electron-energy-loss spectroscopy and x-ray photoelectron spectroscopy. The work function of the TiN/poly-Si stack shows strong dependence on the postmetal deposition annealing conditions. The interfacia/product in TiN/poly-Si interface is inferred as TiSiN, which is beneficial for the whole high-k stack since TiSiN possesses higher work function compared to TiN and poly-Si.