A polymer Mach-Zehnder interferometer (MZI) thermo-optical (TO) switch with low-power consumption is designed and fabricated. To reduce the power consumption, a modulating arm waveguide in the heating region is designed as a suspended waveguide to reduce the heat diffusion. According to the simulation results, compared with a TO switch paired with a conventional waveguide, the suspended waveguide can significantly reduce heat diffusion. The TO switch based on suspended waveguide is fabricated by semiconductor technology. At a 1550-nm wavelength, the power consumption is about 9.3 mW and extinction ratio of the device is 21 dB. The rise and the fall times of the switch are 392 μs and 697 μs, respectively.