Book excerpt: This book discusses in detail the Advanced SPICE Model for GaN HEMTs (ASM-HEMT), a new industry standard model for GaN-based power and RF circuit design. The author describes this new, standard model in detail, covering the different components of the ASM GaN model from fundamental derivations to the implementation in circuit simulation tools. The book also includes a detailed description of parameter extraction steps and model quality tests, which are critically important for effective use of this standard model in circuit simulation and product design. Coverage includes both radio-frequency (RF), and power electronics applications of this model. Practical issues related to measurement data and parameter extraction flow are also discussed, enabling readers easily to adopt this new model for design flow and simulation tools. Describes in detail a new industry standard for GaN-based power and RF circuit design; Includes discussion of practical problems and their solutions in GaN device modeling; Covers both radio-frequency (RF) and power electronics application of GaN technology; Describes modeling of both GaN RF and power devices.