  We measure gate-tuned thermoelectric power of mechanically exfoliated Bi2Se3
thin films in the topological insulator regime. The sign of the thermoelectric
power changes across the charge neutrality point as the majority carrier type
switches from electron to hole, consistent with the ambipolar electric field
effect observed in conductivity and Hall effect measurements. Near charge
neutrality point and at low temperatures, the gate dependent thermoelectric
power follows the semiclassical Mott relation using the expected surface state
density of states, but is larger than expected at high electron doping,
possibly reflecting a large density of states in the bulk gap. The
thermoelectric power factor shows significant enhancement near the
electron-hole puddle carrier density ~ 0.5 x 1012 cm-2 per surface at all
temperatures. Together with the expected reduction of lattice thermal
conductivity in low dimensional structures, the results demonstrate that
nanostructuring and Fermi level tuning of three dimensional topological
insulators can be promising routes to realize efficient thermoelectric devices.
