We report how annealing conditions influence the degree of fluctuation of step edges of step bunching formed by annealing a vicinal GaAs(001) surface in AsH3 and H-2 and ambient. At 700 degrees C, when the partial pressure is high, B steps are straighter than A steps as reported before, however, as the AsH3 partial pressure is decreased, A steps becomes straighter, finally, than the B steps at a partial pressure of 1x10(-2) Torr. This reversal of the type of straight step edges can be explained by considering the (2x4)-c(4x4) phase transition. We will also apply the electron counting model established by Pashley in order to explain the experimental results, and by discussing its usefulness and limitations, finally conclude that we cannot determine the stability of steps only by this model.