The effects of substrate temperature on the deep trap property of In0.52Al0.48As layers grown by molecular beam epitaxy lattice matched on InP substrates have been investigated. Deep level transient spectroscopy measurements have been used to characterize the InAlAs layers and analyze the effects of growth kinetics on the deep traps in the epitaxial layers. Two new deep traps have been found in the samples grown at relatively low growth temperatures, which do not show in the samples grown above 450 °C. The activation energies of these traps are obtained as &Dgr;ET=0.45±0.03 and 0.62±0.02 eV for EI1 and EI2, respectively. A measurable decrease in the densities of EI1 and EI2 was detected following the heat treatment at temperatures above 500 °C.