The effects of alloy disorder on the Schottky barriers at semiconductor-alloy\char21{}metal interfaces are investigated within the defect model of Schottky-barrier formation. The deep levels and the associated wave functions for surface antisite defects, which are believed to be responsible for the barriers considered here, were previously calculated for various III-V semiconductor alloys using the theory of deep levels and treating the alloy host in the virtual-crystal approximation. In the present paper, perturbation theory is used to treat the effect of the random local environment of each defect on these deep levels. For the cation and anion antisite defects at the (110) surfaces of six different III-V semiconductor alloys, the inhomogeneous broadening of the associated deep levels is found to range from nearly 0 to about 0.3 eV, depending on the alloy composition and the material considered. The corresponding effect on the Schottky-barrier heights which result from Fermi-level pinning by these deep levels should be a slight bowing with composition. Typically, this bowing effect is estimated to be of the order of 0.1 eV at intermediate alloy compositions.