The paper presents an nW range gate leakage based Sub-Bandgap Voltage Reference (SUB-BGR) for low-power and high-temperature range IoT applications. It generates a reference voltage of 336mV without incorporating any high-value resistors and working for a high-temperature range of -40◦C to 150◦C. Unlike in conventional SUB-BGRs, the power consumption of the proposed circuit increases only by 9.2 times in the above-mentioned temperature range. Designed in a 65nm CMOS process, the proposed architecture achieves an accuracy of 94ppm/◦C. It achieves an excellent line sensitivity of 0.0066%/V, for a supply range of 0.7V to 4V and PSRR of 89dB at DC and 1V supply. The proposed process-insensitive circuit shows a ±3σ-inaccuracy of 4.305% without additional trimming circuit. It occupies only 0.0851mm2 area while consuming only 2.36nW at 27◦C and 21.74nW at 150◦C at 0.7V supply.