This letter presents a novel 5-GHz transmitter/ receiver (TX/RX) single-pole double-throw (SPDT) switch designed on a silicon substrate. The novelty of this SPDT switch is the possibility it offers to simultaneously design the transmission lines and the active elements, without packaging and consequently its parasitic effects and frequency limitations. The device is intended to be easily integrated into a system with a more complex function, e.g., with amplifiers and antennas. The codesign method offers great flexibility in the positioning and sizing of the active elements, i.e., semiconductor distributed doped areas (ScDDAs), which are integrated n + pp + junctions, in order to obtain the best possible performances in both aspects. A demonstrator provides proof of the concept. In RX-mode, the insertion loss (IL) is 0.9 dB with isolation (ISO) higher than 30 dB. In TX-mode, IL is 2.38 dB and ISO is higher than 43 dB.