X-ray reflectivity and grazing incidence X-ray diffraction (XRD) measurements were performed to characterize the microstructure of homoepitaxial SrTiO3 (STO) films grown by radio-frequency (RF) magnetron sputtering technique. Interference fringes in two sets of disparate period were observed from the reflectivity curves; the fitted result indicates that, in addition to the normal STO layer, there exists a transition layer, which has a smaller mass density than that of STO. X-ray scattering results reveal that an STO film deposited at low temperature (T less than or equal to 300 degreesC) has a density about 10-12% less than that of bulk STO and shows a poor epitaxial relation with the substrate. The presence of oscillation fringes in the diffuse scattering indicates that a conformal relationship exists between the layer and the substrate from deposition at high temperature. The appearance of interference fringes of the crystal truncation rod observed for a film grown at high temperature clearly demonstrates a well epitaxial relationship between the film and the substrate. (C) 2004 Elsevier B.V. All rights reserved.