We present the first results on In0.29Al0.71As which conclusively show a large number of traps that are not in equilibrium with the conduction band at low temperatures, the signature of a DX centerlike defect. From low-temperature gated resistivity, Hall and Shubnikov-de Haas measurements of relaxed, In0.29Al0.71As/In0.3Ga0.7As modulation doped heterostructures, we find a significant negative shift in the threshold voltage, V-g (n(s)--> 0), as the cooling bias is shifted to more negative values. Simultaneously, we observe a decrease in the mobility measured at the two-dimensional electron gas as the cooling bias is decreased, an indication of the "negative U" behavior of DX centers. Finally, we observe Fermi level pinning which we attribute to the occupation of a DX center level. From simulation of the heterostructure at large positive gate biases, and the change in the threshold voltage, we are able calculate the donor ionization energy of this trap to be 320 meV below the InxAl1-xAs conduction-band edge, over twice the depth of the DX center in AlxGa1-xAs.