The electronic states for normally stacked and faultily stacked layers on the GaAs{111} A, B surfaces are calculated by use of the discrete variational X alpha cluster method and the plane wave nonlocal pseudopotential method. The results show that chemical bondings between atoms are not as ionic in the faultily stacked layer of (111) B as they are in the (111)A case, and that on the (111) A surface more attractive Coulomb interaction energy is gained in the faulty stacking layer than in the normal stacking one. These results explain well the more frequent emergence of in-plane faults in the (111) A surface, which is well known in GaAs{111} A, B growth experiments. The total energy calculations also provide quantitative interpretation of such growth features.