Abstract. It has been found at measurements on alternating current that the loop of a thermal hysteresis of semiconductor–metal phase transition in vanadium dioxide VO2 has the asymmetrical multistage form. On a direct current the complex shape of a hysteresis loop wasn't shown. Such behavior for VO2 films can be defined by heterophase nanocrystal structure of vanadium oxide and different type of charge carriers in grains volume and surfaces. The phenomenon is connected with consecutive phase transition in groups of nanocrystallites of the close size. In such films electrical switching with the "tristate" mode for the first time is revealed.