The dc and microwave performance of an InAs channel HEMT is reported. Room-temperature electron mobility as high as 20 200 cm 2 /Vs is measured, with a high carrier concentration of 2.7×10 12 cm -2 . DC extrinsic transconductance of 714 mS/mm is measured and a unity-current-gain cut-off frequency of 50 GHz is obtained for a 1.1-μm gate length HEMT. The success of achieving superior Hall mobility and device performance is strongly dependent on the In x Al 1-x As buffer layer design that changes the lattice constant from lattice-matched In 0.52 Al 0.48 As to In 0.75 Al 0.25 As. The multiple In 0.52 Al 0.48 As/InAs monolayer superlattices buffer achieves the best performance as compared to the step-graded In x Al 1-x As and the uniform In 0.75 Al 0.25 As buffer.