We have fabricated pseudomorphic InGaAs–InAlAs–InP high electron mobility transistors by molecular beam epitaxy with InxGa1−xAs channels graded from x=0.60 to x=0.80. Compared with device profiles using flat x=0.80 channels the channel conductivity is improved by 24%. Hall mobility is improved from 10 750 to 12 200 cm2/V s at 295 K with sheet charge Ns of 3.6×1012 and 3.9×1012 cm−2 for the flat x=0.80 and graded-channel profiles, respectively. Graded-channel devices with 0.1 μm T gates obtained cutoff frequency fT=305 GHz and maximum frequency of oscillation fmax=340 GHz.