A systematic study of the substrate orientation effect on crystalline quality of GaAs grown by molecular beam epitaxy at low substrate temperature (215 °C) was performed using double‐crystal x‐ray diffractometer and transmission electron microscopy. The crystal quality was found to be strongly correlated with substrate orientations. Layers of high crystalline perfection with excess arsenic were obtained on both GaAs(100) and (311)B substrates, while columnar polycrystalline growth was observed on (211)B substrate. The transition from a single crystalline state to a polycrystalline state was clearly demonstrated by a 0.5 &mgr;m GaAs layer on (111)B surface. Surface kinetic factors are believed to play important roles during the low temperature growth. ©1995 American Institute of Physics.