DX centers in molecular‐beam‐epitaxial (MBE) grown Si‐doped AlxGa1-xAs (x=0.3) were characterized by a number of measurement techniques including deep‐level transient spectroscopy (DLTS), temperature dependence of capacitance of Schottky barriers, temperature dependence of Hall electron concentration of modulation‐doped field‐effect‐transistor (MODFET) structures, and temperature dependence of threshold voltage and Schottky gate capacitance of MODFETs. Theoretical models were developed to include the effects of traps (DX centers) on various measurements and extract some trap characteristics by comparison with the experimental results. Internally consistent values for the concentration of shallow donors and traps were obtained from different measurements. The energy position of the trap level obtained from different measurements was 55±10 meV below the conduction band. DLTS measurements gave two peaks with activation energies of 0.40 and 0.47 eV, respectively.