The preferential scattering effect has been investigated for GaN (11¯00) with thickness 2μm grown on 6H-SiC (11¯00) by metal organic vapor phase epitaxy (MOVPE). RBS/channeling experiments were performed using a 1.5MeV 4 He + beam at a scattering angle of 150° under the conditions of [11¯00]-aligned, random, and ±1.2°-off-axis (from the [11¯00]-axis) incidence in the (112¯0) plane. The gallium signals from the surface region decreased for the −1.2°-off-aligned incidence compared with that for +1.2°-off-aligned incidence. In the −1.2°-off-aligned case, the monoatomic strings of gallium are shadowed by that of nitrogen. The quantitative analysis was made by Monte Carlo (MC) simulations of ion trajectories in the GaN (11¯00) crystal. The MC results are in good agreement with the experimental ones, demonstrating that the preferential scattering occurs for GaN consisting of light (N) and heavy (Ga) atoms.