A method of manufacturing a metal gate/high K dielectric gate stack includes the steps of: forming an interfacial layer of SiON or SiO2 on a silicon substrate; depositing a high K dielectric film on the interfacial layer; performing a rapid thermal anneal of the high K dielectric film; depositing a TaN metal gate electrode film on the high K dielectric film; depositing a polysilicon gate layer on the TaN metal gate electrode film, and then depositing a hard mask layer; patterning a photoresist mask, and performing an anisotropic etching of the hard mask layer; removing the photoresist mask, and etching the polysilicon by reactive ion etching with the hard mask as masking layer using a mixed gas of Cl2/HBr; and etching the TaN metal gate electrode/high K dielectric gate stack by reactive ion etching with the hard mask as masking layer using BCl3-based etchant gas.