This paper proposes an ultra-low-power current reference in TSMC 180nm technology. Temperature compensation is achieved by taking the ratio of compensated voltage and an on-chip resistance. This design uses the concept of the back-gate effect of critical MOSFET to generate complementary to absolute temperature (CTAT) voltage. The circuit works from a supply voltage of 0.55V and is designed for a reference current of 5.6nA. Furthermore, a pseudo-differential amplifier (PD-AMP) helps realize low line regulation of 0.022%/V in the supply range of 0.55V to 1.9V. An average temperature coefficient (TC) of 256.07ppm/°C is achieved for mismatch and process variations in Monte-Carlo simulations for 1000 samples over a temperature range of -30°C to 70°C. The circuit consumes only 9.5nW of power (at room temperature and minimum supply voltage), making it suitable for ultra-low-power biomedical applications.