We investigated various surface reconstructions of a GaAs(3 1 1)A surface by using first-principles calculations. The relative stability of the reconstructions was compared by estimating the formation energies taking into account of the chemical potentials of Ga and As. We found that the most stable reconstruction of the (3 1 1)A surface does not satisfy the electron counting model (ECM), although the ECM is a strong guiding principle for determining stable surface reconstructions of Ga-As(1 0 0), (1 1 1)A, and (1 1 0) surfaces. Further investigations indicate that the sp(2)-like-bond formation effectively works at the (3 1 1)A surface. Competition between sp(2)-like-bond formation and As-dimer formation would explain why the ECM is not so effective at this surface. (C) 2004 Elsevier B.V. All rights reserved.