A 2.4 GHz energy harvester for co-integration into a low-power transceiver (TRx) operating at the same frequency is presented. An RF switch decouples the harvester from the TRx and keeps the performance degradation of the TRx low, i.e. 0.2 dB reduced output power in Tx-mode and 0.4 dB reduced sensitivity in Rx-mode. In order to enable the harvester to operate without a DC power supply, an RF switch is used that is passively turned on. The circuit is implemented in a 130 nm CMOS process, and requires a minimum input RF power of −10 dBm. Based on post-layout simulation results the proposed energy harvester achieves a peak efficiency of 22.7% at an input power level of −3 dBm.