A radio frequency (RF) device and its voltage generating circuit are provided. The RF device includes the voltage generating circuit and a RF circuit. The voltage generating circuit receives a RF signal and generates at least one bias voltage related to the RF signal. The RF circuit is used to receive the RF signal. The RF circuit is coupled to the voltage generating circuit to receive the bias voltage. The bias voltage is used to operate the conduction state of at least one RF transmission path of the RF circuit.