The dependence of direct current and microwave performance of InGaAs/InAsP composite channel HEMTs on gate length is presented experimentally. Composite channel HEMTs with gate length from 1.13 mu m to 0.15 mu m were fabricated. Device characterization results showed the extrinsic transconductance increased from 498 mS/mm for 1.13 mu m devices to 889 mS/mm for 0.15 mu m gate devices, while the unity current gain cutoff frequency increased from 24 GHz to 190 GHz. A simple delay time analysis is employed to extract the effective carrier velocity (v(eff)) of the composite channel. The v(eff) is determined to be 1.9 x 10(7) cm/s. To our knowledge, this is the first systematic study on gate length scaling effect of composite channel HEMTs. (c) 2007 Elsevier Ltd. All rights reserved.