AbstractThe development and application of physical models for use in the design of microwave and millimeter‐wave devices and circuits is reviewed. The relative merits of physical models for a variety of active and passive devices are presented together with state‐of‐the‐art results. Particular emphasis is placed on the suitability of the models for use in computer‐aided design software. The techniques used to implement the models in linear and nonlinear designs are examined. Recent developments are presented which indicate the trend toward incorporating these types of models in future design software