A HEMT model is proposed that correctly isolates the access metallization from the intrinsic device to give linear scalability. The model uses a distributed network of intrinsic unit cells composed of lumped elements. The topology of these networks is determined such that a scalable set of parameters is obtained. The parameters for the intrinsic and extrinsic parts of the transistor have been extracted for a GaAs pHEMT and the correct topology derived such that simple scaling rules apply to the unit cell.