We have theoretically investigated poly-Si and metal gates on Hf-related high-k gate dielectrics. First, we have investigated the cause of the substantial threshold voltage (Vth) shifts observed in Hf-related high-k gate stacks with p+poly-Si gates. The oxygen vacancy (Vo) level in ionic HfO2 is located in a relatively higher part of the band gap. If the p+poly-Si-gate is in contact with HfO2, Vo formation in the HfO 2 induces a subsequent electron transfer across the interface because of the higher energy level position of Vo, causing a substantial V th, shifts in p+poly-Si gate MISFETs. Next, we also investigate the microscopic electronic structures at metal gates/HfO2 interfaces. We have found that the wave functions of metal induced gap states (MIGS) have large amplitudes both around Hf and O atoms, which may be the cause of unusual work function behaviors of p-like metals. copyright The Electrochemical Society.