Defects in Si-doped InxAl1-xAs (0<x<0.4) epilayers on GaAs substrates were systematically investigated by deep-level transient spectroscopy. Three electron traps, ranging from 0.22 to 0.89 eV, were observed in InxAl1-xAs grown by molecular beam epitaxy. Their energy levels can be extrapolated from those in the InxAl1-xAs/InP system. A low-temperature-grown buffer layer as well as thermal annealing were found to be capable of reducing the defects in the active layer effectively. (C) 1997 American Institute of Physics.