We studied the thermal reaction of Pd/In0.52Al0.48As contacts using capacitance-voltage (C-V), current-voltage, Auger electron spectroscopy, and x-ray diffraction analyses and compared the results to those for Pd/Al0.25Ga0.75As and Pd/In0.53Ga0.47As contacts. The thickness of InAlAs consumed by the reaction during annealing was calculated directly from the measured C-V profiles. Pd starts to react with InAlAs at a temperature of 100°C, lower than it does with AlGaAs. For thermally annealed Pd/InAlAs and Pd/AlGaAs, both compositional and structural changes were found at the Pd/semiconductor interface. However, in heat-treated Pd/InGaAs samples, compositional changes but no structural changes were observed.