This letter presents a polymer $1{ imes}2$ thermo-optic totalinternal-reflection digital optical switch (TIR-DOS) with an index contrast of 1.5%-${delta}$ operating at low power consumption. The structure of our $1{ imes}2$ TIR-DOS was created by adding a reflection port to that of a conventional multimode filtering variable optical attenuator. To improve the total-internalr-eflection efficiency, a heater offset was applied to the crossing region of multimode waveguides of the TIR-DOS. The fabricated $1{ imes}2$ TIR-DOS shows a low electrical power consumption of 18 mW for an on-off ratio of 35 dB.