@@Half metallic materials have recently attracted much attention due to their high spin polarization, important for research and application in spintronics . As a promising candidate, ultrathin films of magnetite Fe3O4 have motivated numerous investigations on their structure and magnetic properties. In this paper, we report the investigations on growth and magnetic properties of ultrathin monocrystalline Fe3O4 films on GaAs(100) and InAs(100).