We have studied initial growth process of metallic ferromagnetic MnAs thin films on Si(1 1 1) substrates by molecular beam epitaxy (MBE). MBE Growth study was performed under a variety of conditions (i.e. As-4/Mn flux ratio, substrate temperature T-sub) A nearly two-dimensional growth process took place at T-sub approximate to 350 degreesC, under a relatively small As-4/Mn flux ratio (approximate to 1.2), and eventually resulted in the formation of smooth surface. When the As-4/Mn flux ratio was increased at a fixed T-sub (approximate to 350 degreesC) or T-sub was increased at a fixed As-4/Mn flux ratio (approximate to 1.2), the growth mode of MnAs turned to three-dimensional resulting in the formation of islands. Structural characterizations and magnetization properties are presented and the results are discussed in relation to the growth process.