We have theoretically investigated poly-Si and metal gates on Hf-related high-k gate dielectrics. First, we have investigated the cause of the Fermi level pinning (FLP) in Hf-related high-k gate stacks with p+poly-Si gates. The oxygen vacancy (Vo) level in ionic HfO 2 is located in a relatively higher part of the band gap. If the p+poly-Si-gate is in contact with HfO 2, Vo formation in the HfO 2 induces a subsequent electron transfer across the interface because of the higher energy level position of Vo, causing FLP in p+poly-Si gate MISFETs. Next, we investigate the unusual behaviors of metal effective work functions (WFs) on Hf-related high-k gate stacks. We have constructed a a new concept of generalized charge neutrality level. Our theory systematically reproduces the experimentally observed effective WFs of various gate materials, and will become a useful guiding principle for material selection of gate metals.