We reveal the microstructure and dislocation behavior in 20-pair B 0.14 Al 0.86 N/Al 0.70 Ga 0.30 N multiple-stack heterostructures (MSHs) exhibiting an increasing dislocation density along the c-axis, which is attributed to the continuous generation of dislocations (edge and mixed-type) within the individual B 0.14 Al 0.86 N layers. At the MSH interfaces, the threading dislocations were accompanied by a string of V-shape pits extending to the surface, leading to interface roughening and the formation of surface columnar features. Strain maps indicated an approximately 1.5% tensile strain and 1% compressive strain in the B 0.14 Al 0.86 N and Al 0.70 Ga 0.30 N layers, respectively. Twin structures were observed, and the MSH eventually changed from monocrystalline to polycrystalline.