The MOS (Metal Oxide Semiconductor) transistor is the most important building block of modern silicon integrated circuits. This book fills an important gap in the literature by presenting a unified treatment of the operation and modeling of the MOS transistor that is complemented withextensive intuitive discussions.The MOS transistor is the dominant VLSI (Very Large Scale Integration) device, and understanding of this device is mandatory for those people planning a career in device physics and modeling as well as in circuit design. Especially important for university courses,there is a logical, systematic and progressive description that starts with semiconductor fundamentals and builds up to a comprehensive understanding of the basics of MOS transistors. For practicing professionals there are details of nuances observed in MOS transistor behavior, and variousapproaches to modeling these are presented. Detailed derivations are given for modeling dc currents, charges for large-signal operation, small-signal operation at low frequencies and high frequencies, and noise.