Metamorphic high electron mobility transistor structures with high indium content channel layers have been developed on GaAs substrates by solid source molecular beam epitaxy. After grading the buffer layer to In0.64Al0.36As, a single pulse doped structure was grown with a composite In0.65Ga0.35As/In0.80Ga0.20As channel. The RMS surface roughness of a 25 mum x 25 mum area was 11 Angstrom. Cross sectional and plan view transmission electron microscopy measurements indicated planar interfaces and a surface dislocation density < 2 x 10(6) cm(-2). For a sheet density of 2.8 x 10(12) cm(-2), the 300 and 77 K mobilities were 13,500 and 45,400 cm(2)/Vs. The 300K mobility was consistent with increasing mobility with indium channel content and compared favorably with highly strained structures grown on InP substrates. Initial transistor structures with a gate length of 0.14 mum exhibited a current density of 800 mA/mm, a transconductance of 1.5 S/mm, an F-t of 170 GHz, and F-max of 250 GHz. Low voltage operation was demonstrated with a current density of 200 mA/mm obtained at a source-drain bias of 0.1 V: These results are I very encouraging toward extending growth of metamorphic transistor structures to the pseudomorphically forbidden compositional region between InP and InAs. (C) 2002 Elsevier Science B.V. All rights reserved.