InP islands are grown on a GaP substrate by organometallic vapor-phase epitaxy using tertiarybutylphosphine and characterized by atomic force microscopy and transmission electron microscopy. InP grows two-dimensionally at first and then begins to grow three-dimensionally at 1.2 ML. The island sizes are 400 nm in lateral dimension and 100 nm in height at 1.8 ML with the growth temperature of 550 degrees C. The island density increases with increasing InP layer thickness while the island size remains the same. Misfit dislocations are observed in the islands at 1.8 ML growth. By lowering growth temperature to 420 degrees C, the island size becomes as small as 40 nm in the lateral direction, moreover smaller islands without dislocations are obtained. The formation mechanism of large islands is discussed. (C) 1998 Elsevier Science B.V. All rights reserved.