We report a calculation of the electronic properties of GaAs/AlAs (311) superlattices through the Brillouin zone using realistic values of the parameters in a tight-binding Hamiltonian. The nature and the localization of the lowest conduction bands for these low-symmetry structures is investigated and its origin is studied with respect to the layer number. A direct-gap\char21{}to\char21{}indirect-gap transition is evidenced for L=3 nm which is equal to the thickness for which the crossing of \ensuremath{\Gamma}-X states occurs in the (100) superlattices. The in-plane anisotropy of the optical transitions and the relative intensity is found to be dependent on both the layer number and the nature of the states involved in the transition. Comparison with available experimental data is quite satisfactory.