jats:pX-ray diffraction and bright-field transmission electron microscopy are used to investigate the distribution and density of {111}-type stacking faults (SFs) present in a heteroepitaxial zincblende GaN epilayer with high phase purity, grown on a 3C-SiC/Si (001) substrate by metalorganic vapour-phase epitaxy. It is found that the 4° miscut towards the [110] direction of the substrate, which prevents the formation of undesirable antiphase domains, has a profound effect on the relative densities of SFs occurring on the different {111} planes. The two orientations of SFs in the [−110] zone, where the SF inclination angle with the GaN/SiC interface is altered by the 4° miscut, show a significant difference in density, with the steeper (111) SFs being more numerous than the shallower (−1−11) SFs by a factor of ∼5 at 380 nm from the GaN/SiC interface. In contrast, the two orientations of SFs in the [110] zone, which is unaffected by the miscut, have densities comparable with the (−1−11) SFs in the [−110] zone. A simple model, simulating the propagation and annihilation of SFs in zincblende GaN epilayers, reproduces the presence of local SF bunches observed in TEM data. The model also verifies that a difference in the starting density at the GaN/SiC interface of the two orientations of intersecting {111} SFs in the same zone reduces the efficiency of SF annihilation. Hence, (111) SFs have a higher density compared with SFs on the other three {111} planes, due to their preferential formation at the GaN/SiC interface caused by the miscut.</jats:p>