A position controlled or density controlled GaAs microcrystal growth from Ga droplets was attempted using a low energy focused ion beam system. Ga ions from a liquid Ga ion source were accelerated up to 10 kV to produce a focused ion beam. Subsequently the ions were given a positive bias to reduce their kinetic energy by a four-element retarding lens system. The Ga ions with a 30 eV kinetic energy softly landed on a S-terminated GaAs surface and formed a series of Ga droplets or Ga droplets matrix. After initiating the As molecule supply, GaAs microcrystals were found to grow from these Ga droplets. The low energy focused ion beam was also applied to create nucleation sites of Ga droplets on an As-terminated Si (001) surface at 100 eV. Ga droplets with high density were formed on a region where As atoms were removed partially on the Si surface. From these results, the low energy focused ion beam was found useful for position control or density control of GaAs microcrystals on semiconductor materials.