Techniques for increasing efficiency of thermo-optic phase shifters using multi-pass heaters and thermal bridges are provided. In one aspect, a thermo-optic phase shifter device includes: a plurality of optical waveguides formed in an SOI layer over a buried insulator; at least one heating element adjacent to the optical waveguides; and thermal bridges connecting at least one of the optical waveguides directly to the heating element. A method for forming a thermo-optic phase shifter device is also provided.