The authors have successfully fabricated planar micro-optical switch device exploiting the transmitting semiconductor (on) to the reflecting metallic (off) phase transition of thermochromic W(1.4 at. %)-doped VO2 smart coatings and driven by an external voltage. The starting W-doped VO2-coated Al2O3 exhibited infrared transmittance switching about 45%. After the microfabrication, the temperature dependence of electrical resistance of the micro-optical switch showed clearly its well-known semiconductor-to-metallic phase transition at a transition temperature of 36 degrees C. A reversible transmittance switching (on/off) as high as 28 dB was achieved with this device at lambda = 1.55 mu m. In addition, the transmittance switching modulation of the device was demonstrated at 1.55 mu m by switching the micro-optical switch simultaneously with dc and ac voltages. (c) 2007 American Vacuum Society.