The authors report on the self-assembly and the selective-area formation of ferromagnetic MnAs nanoclusters (NCs) on III-V compound semiconductors (1 1 1) B surfaces by metal-organic vapor-phase epitaxy (MOVPE). Hexagonal MnAs NCs with well-defined crystal facets and a high degree of uniformity are self-assembled on planar GaInAs surfaces grown on InP (1 1 1) B substrates. The lateral size and height of typical NCs are 100 and 47 nm, respectively. Lattice images taken by transmission electron microscopy (TEM) show that the top surfaces of the MnAs NCs are atomically flat, and that the interfaces between the NCs and the GaInAs layers are abrupt. We have, in addition, controlled the positions of the MnAs NCs by selective-area MOVPE on GaAs (I 1 1) B substrates partially masked with SiO2 thin films. The hexagonal MnAs NCs do not grow on the SiO2 surfaces, but grow successfully on the GaAs ones, under a relatively high growth temperature condition of 850 degrees C. (C) 2007 Elsevier B.V. All rights reserved.