A selective growth of GaAs microcrystals was demonstrated on a Se-terminated GaAlAs surface. Ga molecules were supplied to the Se-terminated GaAlAs surface at first. The surface consisted of Ga droplets and bared Se-terminated GaAlAs surface. After the following As molecule supply to the surface, a selective GaAs microcrystal growth from Ga droplets was observed. The cross sectional investigations by the high resolution electron microscope revealed epitaxial growth of GaAs microcrystals with (111) facets and a possibility of (GaAl)2Se3 layer formation at the GaAs/Se-terminated GaAlAs interface.