(Ba,Sr)TiO3 (BST) thin films were prepared on Pt/SiO2/Si substrates by the pulse injection chemical vapor deposition (CVD) process, in which the vapor of precursors was allowed to flow periodically into the reaction chamber. The dielectric constants of BST thin films, which were deposited by pulse injection CVD, were slightly higher than those of continuous BST thin films. In addition, the leakage currents were lowered by an order of magnitude. 35 nm thick BST thin films, deposited by pulse injection CVD and postannealed at 600 °C under O2 atmosphere for 30 min, showed a SiO2 equivalent thickness of 0.64 nm, a dielectric dissipation factor less than 0.5%, and a leakage current density of 1×10-7 A/cm2 at +1.5 V bias. The improvement in the electrical properties of pulse BST thin films seems to originate from better crystallinity and less carbon contamination during the pulse deposition process.© 1998 American Institute of Physics.