A 433 MHz wake-up-receiver has been designed and fabricated in 250 nm BiCMOS technology. In a novel approach, an off-chip switched SAW resonator accumulates energy from the radio wave and subsequently emits it as a voltage pulse. This mechanism delivers passive amplification and filtering of the input signal without additional power consumption. The integrated analog frontend evaluates the height of the voltage pulse in the context of on-off keying. The analog frontend circuitry draws 46 µA - 70 µA (meas.) from a 2.5 V supply. With a bitrate of 10 kbps, the energy per bit efficiency amounts to 17.4 nJ/bit without duty cycling. The active chip area measures 370 µm × 210 µm, In this implementation, a passive pulse voltage amplification of up to 24 dB and an input sensitivity of -78 dBm were measured. A detailed analysis of the switched SAW network in a realistic application shows that a passive voltage amplification of 32 dB is attainable. The functionality of the analog frontend has been verified by measurements.