Polycrystalline SrTiO₃ thin films have been prepared on Si(100) substrates by RF magnetron sputtering. The films were deposited at 400 degrees C and were annealed at 600 degrees C. The films had a dense microstructure with fine grains. The electrical properties of the films were dramatically controlled with annealing. From the result of the capacitance-voltage (C-V) characteristics the dielectric constant and the flat band voltage of the annealed films were measured to be 75 and -0.31 V, respectively. These oxide thin films with high dielectric constant are potentially useful in ULSI applications.