High electron mobility transistor structures containing Inx(AlGa)1-xAs and InxGa1-xAs device layers with X=0.3–0.4 were grown on metamorphic buffer layers on GaAs substrates. The structures exhibited good flatness with a root mean square roughness of 9 Å. Cross-sectional transmission electron micrographs indicated that the threading dislocations from metamorphic growth were contained in the graded buffer layer. For double pulse doped structures, sheet densities up to 4×1012 cm-2 were readily achieved. Room temperature mobilities of 8600–8800 cm2/V s were obtained using In0.42Ga0.58As channel layers. Photoluminescence measurements of the InGaAs channel layer in metamorphic and pseudomorphic structures showed no significant reduction in room temperature luminescence intensity due to metamorphic growth. Transistor structures of the same device geometry were fabricated from both metamorphic and pseudomorphic GaAs high electron mobility transistor structures. At 25 GHz, the metamorphic device produced a 3 dB higher associated gain with a 0.4 dB lower noise figure. Device operation under current drive was demonstrated at 5–6 V bias which represents a significant improvement over InP-based devices. A state-of-the-art power density of 0.9 W/mm was obtained at 35 GHz. © 2000 American Vacuum Society.