MOSFET is a key component for integrated circuits which controls and helps the human activities in modern society. The demands for high performance and low power MOSFETs become stronger and stronger with the progress of smart society. Gate stack is the most critical element of the MOSFETs which controls its operation. In this report, after the explanation of the overall basics of the gate stack technology, recent status of the gate stack R & D are reviewed, focusing on that for high-k/metal gate stack.