The microstructure of GaN(Si)/AlInN multiple quantum wells grown on GaN/Al2O3 (0001) templates by metalorganic vapor-phase epitaxy has been investigated using transmission electron microscopy and associated techniques. Dodecagon-shape V-defects with hexagonal apexes, which nucleate on screw-component threading dislocations, are observed at the film surface. The hexagonal apexes are bounded by {11 (1) under bar1} planes, whereas the dodecagons are bounded by {10 (1) under bar1} and {11 (2) under bar1} planes, where the {10 (1) under bar1} facets are generated from the edges between adjacent {11 (2) under bar1} planes. Indium segregation is observed along these edges. A possible reason for formation of these defects is briefly discussed. (C) 2010 American Institute of Physics. [doi:10.1063/1.3502483]