Linearization of power amplifiers in communication systems is an eternal and challenging topic. This topic has recently attracted particular attention due to the widespread use of non-constant envelope modulation schemes which require highly linear and very low distortion power amplifiers. The work in this book is dedicated to solve the linearity problem faced by millimeter-wave power amplifiers, which is lack of effective solutions in this field. An amplifier-based linearization design method was proposed firstly. Two amplifier-based predistortion circuits have been investigated. One uses a fixed bias and the other utilizes a nonlinear signal- dependent bias. One major contribution in this book is the proposal of an original predistortion circuit design methodology derived from frequency to signal amplitude transformation by transforming RLC circuits with predetermined transfer functions. All these linearization methods have been demonstrated through simulations in GaAs pHEMT to offer better performances than existing predistortion methods and have a broad prospect for applications.