We have utilized the isothermal capacitance transient spectroscopy and modulated function waveform analysis to investigate the deep levels and DX centers in molecular beam epitaxially grown AlxGa1−xAs/GaAs Schottky diodes deposited onn+GaAs, with Al composition ranging fromx=0 to 0.5, and implanted with Si. In the concentration rangex=0.19 to 0.50, two major electron trap levels (E1andE2) were detected, which gradually changed with composition. For example,E1changed from 0.393 to 0.339 eV andE2changed from 0.136 to 0.287 eV. However, in pure GaAs, three major trap levels with energyE1(hole)=0.226 eV,E2(electron)=0.496 eV, andE3(EL2)=0.74 eV were observed. Apparently, these levels are governed by the deep levels known as DX centers.