There is a method of controlling nucleation and lateral growth using the three-dimensional (3D) and two-dimensional (2D) growth modes to reduce the dislocation density. We performed 3D–2D-AlN growth on 6H-SiC substrates to obtain high-quality and crack-free AlN layers by low-pressure hydride vapor phase epitaxy (LP-HVPE). First, we performed 3D-AlN growth directly on a 6H-SiC substrate. With increasing V/III ratio, the AlN island density decreased and the grain size increased. Second, 3D–2D-AlN layers were grown directly on a 6H-SiC substrate. With increasing the V/III ratio of 3D-AlN, the crystalline qualities of the 3D–2D-AlN layer were improved. Third, we performed 3D–2D-AlN growth on a trench-patterned 6H-SiC substrate. The crack density was reduced to relax the stress by voids. We also evaluated the threading dislocation density by using molten KOH/NaOH etching. As a result, the estimated edge dislocation density of the 3D–2D-AlN sample was 3.9 × 108 cm−2.