A multistage SiO2/SiON/SiO2 2x2 optical switch utilizing the multimode interference effect is proposed. The entire switching is realized based on the thermo-optic effect of SiO2/SiON dielectric layers. The heating power required to switch the optical beam from bar to cross state is determined to be similar to 0.82 W. The highest extinction coefficient achieved during the optical switching between bar and cross output channels is in excess of 13 dB. Furthermore, the experimental results show that the rise and fall times of this device measured approximately 360 and 395 mu s, respectively.