We have investigated the deep electronic levels in n-In0.35Ga0.65As epitaxial layers grown by molecular beam epitaxy (MBE) on graded InxGa1-xAs buffer/GaAs structures. InxGa1-xAs buffer layers with linear, parabolic and power composition grading law, respectively have been considered. The dependence of the deep levels distribution on the buffer grading law as well as on growth parameters such as the growth temperature and use of As-2 or As-4 beams is reported. (C) 1998 Elsevier Science Ltd. All rights reserved.