Low-voltage hybrid silicon-germanium bandgap reference circuits that can defy the voltage scaling limits of those realized in purely silicon-based technologies are implemented. Germanium diodes replace silicon diodes in two conventional bandgap reference circuits fabricated in a 0.18-um Si CMOS process, and experimental results validate the benefit of exploiting a low bandgap material. The output references are measured as 670 mV and 310 mV with 9.3 mV (287 ppm/°C) and 4.6 mV (302 ppm/°C) variation, respectively, over 5 ~ 56 °C. In addition, the high temperature characteristics limiting the operation range related to low bandgap are investigated.