Micro-thermoelectric (TE) devices have a great potential for future applications in the field of energy harvesting to power autonomous sensors. Bi₂Te₃ sputtered at elevated substrate temperatures exhibits a high figure of merit (ZT) suitable for the fabrication of micro-TE devices. However, a lift-off process that does not allow higher substrate temperatures is often used, and although Bi₂Te₃ is a well-studied TE material, it lacks full ZT characterization of thin films. Herein, the full TE characterization of sputtered Bi₂Te₃ thin films is presented, including the charge carrier concentration and mobility, which are deposited at room temperature and postannealed between 150 and 300 °C. The influence of the annealing time and temperature is investigated on a 90 nm-thick Bi₂Te₃ film. A maximum ZT of 0.20 is found, which results from the increasing crystallinity and reduction of point defects. To investigate the thickness dependency, Bi₂Te₃ films with thicknesses of 90, 170, 350, and 470 nm are annealed at 250 °C. A maximum ZT value of 0.26 is observed for the 350 nm Bi₂Te₃ film. Furthermore, it can be shown that with increasing film thickness, the annealing time has to be increased to maximize ZT.