We report that the Te donor forms a deep level and acts as aDXcenter in In1−xGaxAsyP1−y/GaAs0.61P0.39. The characteristics of Te‐related deep level is investigated by deep‐level transient spectroscopy and thermally stimulated capacitance measurements. The deep level has a thermal activation energy of 0.14±0.01 eV regardless of the alloy composition of In1−xGaxAsyP1−y. Persistent photoconductivity is observed at low temperature in all Te‐doped In1−xGaxAsyP1−y/GaAs0.61P0.39samples. The compositional dependence of deep trap density is explained by the energy difference between the conduction band minimum and theDXlevel. ©1996 American Institute of Physics.