This paper demonstrates a millimeter-wave RF-to-DC converter based on Schottky-barrier diodes using 0.18-mu m CMOS technology. The Schottky-barrier diode has a cutoff frequency of 400 GHz and a low turn-on voltage of 0.3 V. In the RF-to-DC quadrupler, the difference in turn-on voltages between the Schottky-barrier diode and n-well to p-substrate parasitic pn junction prevents the pn junction from turning on with an effect similar to the Schottky diode clamp in Schottky TTL circuits. The input matching has a better than 10 dB return loss from 50 GHz to 100 GHz. The RF-to-DC quadrupler generates a 3.15 V DC voltage at 84 GHz.