MBE growth of GaAs mesa structure consisting of (0 0 1) top and (1 1 1)B side surfaces was studied and the ratio of growth rate on (1 1 1)B facet to that on (0 0 1) was measured in various growth conditions. The value changed drastically, from 0 to 0.8, depending on the growth conditions. It was found that complete growth elimination occurred on (1 1 1)B facet by decreasing incident Ga flux and suppressing 2D-nucleation. We obtained various information from these experiments about elementary process of GaAs MBE, including critical Ga adatom concentration for 2D-nucleation on (1 1 1)B surface and (1 1 1)B-(0 0 1) inter-surface diffusion.