A conception of thermo-optic switched directional coupler with reversed Δβ is proposed and a testing device with two paires of electric heaters has been fabricated on glass substrate. At 1 kHz square wave voltage modulation, analyzing optical output power from the device by using a high speed 12-bit A/D converter connected with a computer, shows that both a bar-state and a cross-state have been obtained. Because glass waveguides are optical damage-free, polarization-insen sitive, and easy to fabricate, the device can be widely nsed in the oases that do not require high speeds.