We designed and fabricated a low-loss transmission line structure with through-silicon vias (TSVs) for use in the millimeter-wave region for three-dimensional packaging of radio frequency microelectromechanical system devices. High-frequency simulations were used to determine the optimum transmission line structure. A transformer was employed to compensate for the impedance mismatch between the TSVs and the coplanar waveguide. The proposed structure was fabricated using a combination of surface micromachining and the molten solder ejection method. The electrical properties of the TSVs and the transmission line were measured, and a low insertion loss of 0.7dB at 80GHz was achieved.