The band structures of some zincblende III-V semiconductor alloys are calculated beyond the virtual crystal approximation (VCA) using the empirical pseudopotential method (EPM). Our results show that the calculated optical bandgap bowing parameter agree with the experiment only when going beyond the VCA. We also found that the direct bandgap (Gamma --> Gamma) bowing factor becomes generally larger on going from alloys with small lattice mismatches to those with larger ones. (C) 2002 Elsevier Science B.V. All rights reserved.