We report a simple and low-cost method to fabricate SU-8-based polymer waveguide devices. The influence of hard-baking temperature on SU-8 polymer treated with or without UV radiation was investigated in detail. Based on these properties, the straight type, Y branch type, March-Zehnder (M-Z) type and 1 × 4 splitter waveguides were successfully fabricated. And a polymeric thermal-optic (TO) switch with M-Z type waveguide was also fabricated by this method. The device exhibits low power consumption of less than 6.4 mW, fast rise time of about 149.3 µs and fast fall time of about 139.3 µs. The experimental results showed that this method can bypass the need for complex lithography and provide high resolution and fine waveguide quality desired for TO switches as well as other planar lightwave devices.