Deep levels, the so-called DX centers, in the AlxGa1-xAs alloy system grown by liquid-phase epitaxy (LPE) were investigated by junction-capacitance spectroscopy. The dependence of the activation energy of the DX center in Sn-doped AlxGa1-xAs on the alloy composition was determined by DLTS. This dependence seems to reflect the change in the nature of the conduction bands in this alloy system. The other donor species studied: Si, Te and Se, were also found to form DX centers. An anomalously high concentration of DX centers was determined using low-temperature C-V techniques.