Heteroepitaxial Y 2 O 3 films on Si(100) have been grown by the technique of reactive ionized cluster beam (ICE) deposition. The composition of deposited film is investigated by using the X-ray photoelectron spectroscopy (XPS). It was found that the composition ratio of Y to O is 1 to 1.46. Using reflection high energy electron diffraction (RHEED) and glancing angle X-ray diffraction (GXRD), we study the crystallinity of the films. It was noticed that the orientation of deposited film is mainly determined by the substrate temperature and the cluster acceleration energy. We also found that, without acceleration below 800°C, Y 2 O 3 films were grown as polycrystalline. Under the condition of 5 kV acceleration voltage above 650°C, we noticed the heteroepitaxial growth of Y 2 O 3 film on Si(100) substrate. The epitaxial relationship between Y 2 O 3 and Si(100) is presented as Y 2 O 3 (110)//Si(100) and Y 2 O 3 [110]//Si[100] or Y 2 O 3 (110)//Si(100) and Y 2 O 3 [100]//Si[100].