GaN /AlGaN transistors are being developed for a variety of RF electronic and high temperature electronics applications that will replace GaAs and Silicon based devices and amplifiers for commercial and military applications. In this paper, we present GaN/AlGaN based HEMT device architectures on SiC substrates with simulation and modeling results. The HEMT epitaxial layers were grown using RF Plasma Assisted MBE Technique. This approach has demonstrated very uniform epitaxial layers. The key to high performance HEMTs is the ability to grow high quality (Al)GaN buffer layers. Details of the electrical and optical characteristics of the HEMT wafers are presented. In addition, we will present results on an modified (ICP) etching technique that allows for low damage device processing and improved reliability.