The homoepitaxy of GaAs on (631)-oriented substrates has been studied as a function of the growth temperature. We observed the spontaneous formation of a high density of large scale features on the surface. The hilly like features are elongated towards the [-5,9,3] direction. When the growth temperature was varied from 490 to 580°C the hillocks length exponentially increases from 1.8 to 4.3 µm, their height linearly increases from 35 to 50 nm, and the density exponentially decreases from 2.8×10 6 to 3×10 5 /cm 2 . The hillocks formation is discussed in terms of adatoms diffusion anisotropy, sticking properties at step edges, and Ehrlich–Schwoebel diffusion barriers.