We demonstrate the successful formation of ferromagnetic MnAs nanoclusters, self-assembled on GaInAs (I 1 1) B surfaces by metalorganic vapor phase epitaxy (MOVPE). The hexagonal MnAs nanoclusters show strong ferromagnetic coupling at room temperature when the external magnetic fields are applied in a direction parallel to the InP (I 1 1) B wafer planes. We have found that, on GaInAs/InP (I 1 1) B layers, the size and density of the MnAs nanoclusters strongly depend on the MOVPE growth conditions. The averaged height of the nanoclusters is decreased from 250 to 61 nm with increasing V/Mn ratios in a supply gas from 60 to 750, whereas their density is increased from 10(7) to 10(8) cm(-2). It is increased from 66 to 319 nm with increasing growth temperatures from 550 to 700 degrees C, whereas the density is decreased from 10(8) to 10(7) cm(-2). The size and density of the MnAs nanoclusters are controllable by optimizing MOVPE growth conditions, such as growth temperatures, V/Mn ratios and growth time. (c) 2006 Elsevier B.V. All rights reserved.