Orientation -selective-epitaxially grown CeO2 layers on Si(100) substrates are characterized by x-ray diffraction (XRD) and cross-sectional transmission electron microscopy (XTEM). XRD analyses prove how diffraction intensities of CeO2 (200) and (220) peaks vary depending on substrate bias under which the layers grew. It is confirmed that (200) and (220) peaks reach maxima at +/- 15 and 0 V biases, respectively, where they are pure single crystalline of respective orientations. Samples grown at other bias have both (200) and (220) peaks, whose peak intensity ratio varies as the bias voltage departs from above three values. These results agree well with the reported results by reflection high energy electron diffraction analyses. XTEM observations are carried out utilizing focused ion beam technology in sample fabrication. In CeO2(110)/Si(100) samples, interfacial amorphous layers are seen, which are similar with commonly reported results. XTEM lattice images clarify the nonexistence of interfacial amorphous layers in CeO2(110)/Si(100), which owes to the two step growth method: metal Ce layer deposition and silicidation process followed by CeO2 layer deposition. (c) 2007 American Vacuum Society.