Uniformly Si doped GaAs/Al0.33Ga0.67As multilayer structures have been studied by deep level transient spectroscopy (DLTS) and photocapacitance measurements. DLTS spectra showed five peaks which are related to defects in the GaAs layers. The concentration of these defects decreased with increasing layer thickness. An additional peak, which has been observed with forward bias filling pulses, is suggested to be related to defects near the surface, most probably due to defect accumulation in multilayers. Their emission and capture properties as well as photoionization cross sections have been studied. Evidence is provided that the emission and filling processes of these deep levels are modified due to the energy quantization in the conduction band and the carrier transport through the quantum structures. NoDXcenter related DLTS peaks or other features like persistent photoconductivity effects have been observed in any of our samples. ©1996 American Institute of Physics.