This 62-page handbook uses insight to explain how metal–oxide–semiconductor (MOS) field-effect transistors (FETs) block and conduct current in sub-threshold, weak inversion, and inversion. It describes how MOSFETs accumulate, deplete, and invert their channels and how they saturate their currents in sub-threshold and inversion. It also discusses body effect, how gate–channel oxide capacitance distributes across operating regions, and short-channel effects, like drain-induced barrier lowering (DIBL), surface scattering, hot-electron injection, oxide-surface ejections, velocity saturation, and impact ionization and avalanche. Discussions extend to varactors, MOS diodes, lightly doped drains (LDD), diffused-channel MOSFETs (DMOS), junction isolation, substrate MOSFETs, welled MOSFETs, and electronic and systemic noise coupling and injection. Illustrative figures, equations, and examples complement discussions throughout.