In0.52Al0.48As/InxGa1-xAsyP1-y/In0.52Al0.48As high electron-mobility transistors with single-channel and triple-channel structures were successfully fabricated by low-pressure metal-organic chemical-vapor deposition. The single-channel structure exhibits higher transconductance and drain-source saturation current than the triple-channel due to the higher average-carrier saturation velocity and sheet-carrier concentration of the In0.53Ga0.47As channel. The triple-channel structure is employed to take advantage of both the high electron mobility of In0.53Ga0.47As and the low ionization coefficient of InP. A third quaternary In0.72Ga0.28As0.61P0.39 (E-g similar to 0.95 eV) layer is introduced between In0.53Ga0.47As (E-g similar to 0.75 eV) and InP (E-g similar to 1.35 eV) channels to improve the electron-transport characteristics. Experimentally, the investigated triple-channel structure exhibits a low leakage current, a high breakdown voltages and a high linear-operation regime. (C) 2004 American Vacuum Society.