HEMTs and pHEMTS are important new semiconductor devices that have a high performance profile. They are also low noise. GAN HEMTs are being used in high power RFMW power amplifiers. pHemts are also being used in high frequency and low noise amplifiers. The operation of the HEMT is not immediately intuitive. This post seeks to provide a basic description of the backbone of the HEMT operation. Following posts will explore more details of the HEMTs/pHemts. Interested parties may access a detailed description from the Signal Processing Group Inc., website under the “complemntary items ” menu.