Localized and fast temperature measurement is essential for devices. One promising approach is the use of materials that undergo a phase transition with temperature. However, there has not been much systematic research on how well phase transition materials can follow rapid temperature changes. The reason is that it is technically difficult to control temperatures quickly and precisely. We have investigated the phase transition of vanadium dioxide (VO₂), a typical phase transition material, by using it as a channel in FET and have systematically investigated its rate by controlling the phase transition by the gate voltage. The phase transition rate increases exponentially with the difference of electron accumulations at the gate interface, and the rate of increase indicates that a population of more than 1000 vanadium atoms is responsible for the elementary process of the transition. This is the first study to clarify the transient characteristics of not only the metallic transition but also the insulation transition, and it is an important finding for the local temperature measurement using phase transition materials.