Al0.34Ga0.66As amorphous thin films doped with Si have been prepared for studying common features of DX type of defects in crystalline and amorphous semiconductors. We have observed in these materials the persistent photoconductivity (PPC) effect at T < 250 K. The four energies which characterize the DX levels in these materials have been determined. A large Stokes shift with a value which is comparable with that of DX centers in crystalline AlxGa1-xAs has been observed. Our results suggest that the existence of the DX centers as well as of PPC is not simply a consequence of the band structure. Our results also suggest that there may exist a common description for DX type defects in crystalline and amorphous semiconductors.