The growth of high quality, gate-tunable topological insulator Bi2Se3 thin films on SrTiO3 substrates by molecular beam epitaxy is reported in this paper. The optimized substrate preparation procedures are critical for obtaining undoped Bi2Se3 thin films with sufficiently low carrier densities while maintaining the strong dielectric strength of the substrates. The large tunability in chemical potential is manifested in the greatly enhanced longitudinal resistivity and the reversal of the sign of the Hall resistivity at negative back-gate voltages. These thin films provide a convenient basis for fabrication of hybrid devices consisting of gate-tunable topological insulators and other materials such as a superconductor and a ferromagnet.