||High electron mobility transistors (HEMT) and their integration into advanced monolithic integrated circuits is the enabling technology for modern microwave/millimeter-wave system applications. Although InP-based devices have been shown to have superior performance in high power applications, these high-performance devices are normally grown on high-cost and fragile InP substrates by molecula-beam epitaxy (MBE). In the past few years, metamorphic HEMT (MHEMT) technologies have matured and successfully transferred from laboratories to 6” GaAs foundries, and high quality devices that can be directly grown and fabricated on GaAs or Si substrates by metal-organic chemical vapor deposition (MOCVD), will allow for high volume production. Further development of the technology will lead to continuous use of the traditional and ever improving manufacturing technologies for Si, with integrated III-V devices on the same chip as the critical components. This thesis focuses on the fabrication of MOCVD grown AlInAs/GaInAs metamorphic HEMT on GaAs and Si substrates. The fabrication processes are discussed. The fabricated devices were characterized and found to have excellent DC and RF performance. A new approach to fabricate enhancement mode (E-mode) InP-based HEMT by using CF4 plasma treatment process was also developed. E-mode AlInAs/GaInAs MHEMT fabricated by this technique was characterized to have better pinch off ability, lower gate leakage current in both reverse and forward gate bias and no significant degradation in small signal RF performance.