Vanadium dioxide (VO ₂ ) thin films have unique insulator to metal transition above the critical temperature of 68 °C. In this study, VO ₂ thin films were deposited on a sapphire substrate for thermally controllable RF/microwave devices such as switches, limiters and resonators. The selectively deposited VO ₂ thin film based devices showed ∼2 kΩ at room temperature and less than 2 Ω at 70 °C. These thermally controlled varistors were utilized in shunt as well as series configurations for microwave switching and in resonant structures. Switching devices designed using a VO ₂ shunt varistor showed good isolation (>20 dB) and low insertion loss (<1 dB) up to 20 GHz. This paper presents two types of shunt varistor devices designed and fabricated on sapphire substrates.