An ultra-low power and area, CMOS based temperature sensor with digital interface for military application (− 55 to 125 °C) is introduced. The sensor employs a proportional to absolute temperature current generator operating in sub-threshold region, and a novel signal-conditioning circuitry. A low power and area sigma-delta analog-to-digital converter ( $$\varSigma \varDelta$$ -ADC) is used for temperature to digital conversion. The $$\varSigma \varDelta$$ -ADC is realized using second order $$\varSigma \varDelta$$ modulator, where a self-biased, gain-boosted class-C inverter is shared between two stages for low power and low area, besides achieving a resolution of 12-bits. The overall sensor is realized in 65 nm CMOS standard process and its performance is validated using post-layout simulations, considering worst case. After one-trim, the sensor achieves an accuracy of $$\pm \,0.25\,^{\circ }$$ C, while having a resolution of 0.18 °C and a resolution figure of merit of 0.0058 nJK2. The sensor operates at a power supply of 1-V, consuming power of 27.8 μW and an area of 0.0033 mm2 (excluding digital filter).