MOCVD-grown AlN/GaN superlattices (SL) with different thickness of the well and barrier are investigated by transmission electron microscopy in low-magnification and high-resolution modes. Growth-induced defects are observed in some places causing different degree of disturbances of the regularity of the SLs. The SL grown with a thickness of the AlN barrier higher than the critical thickness hc for coherent growth reveals 2D growth of AlN platelets that give rise to cusps or irregularities at the interfaces. The SL with thickness of the GaN and AlN layers lower than hc is coherently grown. There is some evidence of dot-like structures formation in separate areas due to the large strain field present. © 2003 Elsevier B.V. All rights reserved.