A small and fast self-holding 2 × 2 optical switch using phase change material is proposed. This switch is based on a directional coupler in which a short waveguide made of a phase-change material (PCM) is sandwiched between two Si waveguides. The characteristics of the proposed switch were simulated by a beam propagation method (BPM). This switch can be as small as 3µm × 21µm because the change in the refractive index of PCMs between the crystalline and amorphous states is very large; in addition, by utilizing the self-holding characteristics, it has the potential for low power consumption. The loss and the crosstalk were calculated to be 2.5dB and -20.4dB in the bar state and 1.3dB and -14.3dB in the cross state, respectively.