This paper proposes a 2.4-GHz pre-bias RF energy harvesting rectifier with -35-dBm sensitivity for self-powered chips of wireless sensor networks (WSNs) for Internet of Things (IoT) applications. For high sensitivity, a pre-bias topology is presented by designing pre-stage and drive-stage rectifiers separately with multiple antennas. The pre-stage and the bias circuit just provide a proper bias voltage without driving loads. At single drive-stage configuration, -35-dBm sensitivity can be achieved with 2.4-GHz RF input power, 10-MΩ output load and 0.5-V continuous output voltage. When an 1% duty-cycled operating mode is adopted, 25-μW power can be supplied intermittently with 0.5-V output voltage. This proposed circuit is designed in 0.18-μm standard CMOS process.