A resistor-less nano-Watt voltage reference circuit using only Metal-Oxide Semiconductor Field Effect Transistors (MOSFETs) is presented. To ensure low-power operation, the circuit is biased in the subthreshold region. The reference voltage is generated by using a temperature dependent current generated from a modified Oguey Current Source to bias a diode-connected MOSFET. The proposed circuit is simulated using a 65 nm Complimentary Metal-Oxide Semiconductor (CMOS) process. The circuit can operate from 0.65 to 2.5 V in the temperature range from -30 to 80 oC. The circuit achieves a temperature coefficient of 19.3 ppm/C while consuming 3.64 nW power at room temperature. The line sensitivity of the circuit is 0.0026 %/V and the power supply rejection ratio (PSRR) is -75 dB at 100 Hz. The voltage reference occupies 0.0063 mm2 of area.