We grew epitaxial SrTiO3 (STO) thin films on (001) LaAlO3 substrates via a two-step procedure using pulsed laser deposition and studied them with transmission electron microscopy in plane-view and cross-sectional samples. We found that partial misfit dislocations are the main interfacial defects, whereas planar defects are the main defects in STO films. Our results suggest that a three-dimensional island mode dominates the growth of the STO film.