GaN was grown by low angle incidence microchannel epitaxy (LAIMCE) using NH 3 -based metal-organic molecular beam epitaxy (NH 3 -based MOMBE). The growth mechanism was studied by varying the growth temperature and time. The effect of the incidence direction of precursors on lateral growth was also investigated by comparing the results obtained when precursors were supplied perpendicular and parallel to the openings in the mask. The thickness and width of lateral growth were largely influenced by the formation of a facet on the surface, which frequently terminates further growth. For example, a sample grown at 700 1C with a perpendicular supply of precursors stopped growing both vertically and laterally after a certain time despite continuous supply of the precursors. On the other hand, a sample grown at 820 1C with a parallel supply of precursors exhibited stable growth, and its width increased continuously with time. This is because inter-surface diffusion of adatoms occurred from the top to the sides, which enhanced the width of lateral growth. In contrast, low angle incidence supply of molecular beams perpendicular to the openings resulted in a Ga-rich condition on the side and formed the side facet, which terminated further LAIMCE growth.