A novel LC-based spiral transmission line consisting of only one three-turn inductor and two capacitors is proposed for the first time. Based on this structure, the function of the quarter-wavelength transmission line can be realized with smaller area and less insertion loss compared with conventional micro-strip transmission lines. By using the LC-based spiral transmission line, a compact Single Pole Double Throw (SPDT) switch is implemented in 65-nm CMOS. The SPDT switch occupies only 0.028 mm² with measured 1.3-dB insertion loss and 24-dB isolation at 28 GHz.