InSb thin films were grown on Si (001) substrate via both conventional one-step growth and two-step growth methods by molecular beam epitaxy. The effect of two-step growth was investigated by transmission electron microscopy. A lot of planar defects and surface steps were observed in the InSb thin film directly grown on buffer layer. The crystalline quality of the InSb thin film was improved when it was grown via two-step growth. The low-temperature InSb initiation layer of two-step growth relieved a misfit strain by generating 90 degrees misfit dislocations and obstructed the propagation of defects by trapping at the interface. (c) 2006 American Institute of Physics.