The conduction band offset differences near the Gamma point of the lowest Gamma(1)-like conduction band of GaAs/AlAs heterostructures due to spin splittings were obtained for different k values in both <110> and <100> directions. The conduction band offset differences vanish along the <100> directions and follow a cubic dependence for small wave vectors along <110> directions. The valence band offset calculated in the sp(3)s* configuration using the recently reformulated tight binding method is 0.46 eV in good agreement with experiments. (C) 2004 Elsevier Ltd. All rights reserved.