Betavoltaic transducer devices are widely used in applications requiring ultra-long life, high energy density, and self-powered power supplies. The purpose of this paper is to prepare CdTe-based betavoltaic transducer devices based on magnetron sputtering and to enhance their performance. We explored the effects of three factors on device performance: the thickness of CdTe, annealing temperature, and electrode shape. The thickness of polycrystalline CdTe film is most important for the CdTe device. Both the annealing temperature of CdTe and the electrode shape play significant roles in the optimization of device performance. Finally, the device with an open-circuit voltage of 423.1 mV and short-circuit current density of 2.45 nA/cm2 has been obtained when CdTe film is 200 nm, the annealing temperature is 385 °C, and the specific electrode shape is adopted. This result is the highest performance to date for a CdTe-based betavoltaic transducer device loaded with a 3H radioactive source.