A passive wireless switch circuit and related apparatus are provided. In examples discussed herein, the passive wireless switch circuit includes a microelectromechanical systems (MEMS) switch(es) configured to be closed when receiving a constant voltage(s) that exceeds a defined threshold voltage (e.g., 30-50 V). The passive wireless switch circuit is configured to convert a radio frequency (RF) voltage(s), which may be harvested from an RF signal(s) received via an antenna(s) in a selected frequency bandwidth(s), into the constant voltage higher than the defined threshold voltage to close the MEMS switch(es). As such, it may be possible to eliminate active components and/or circuits from the passive wireless switch circuit, thus helping to reduce leakage and power consumption. As a result, it may be possible to provide the passive wireless switch circuit in a low power apparatus for supporting such applications as the Internet-of-Things (IoT).