In this paper, a low-power CMOS smart temperature sensor is presented. The temperature information extracted using substrate PNP transistors is digitized with a resolution of 0.03°C using a precision switched-capacitor (SC) incremental ∆Σ A/D converter. After batch calibration, an inaccuracy of ±0.25°C (±3σ) from-70°C to 130°C is obtained. This represents a twofold improvement compared to the state-ofthe-art. After individual calibration at room temperature, an inaccuracy better than ±0.1°C over the military temperature range is obtained, which is in-line with the state-of-the-art. This performance is achieved at a power consumption of 65µW during a measurement time of 100ms, by optimizing the power/inaccuracy trade-offs, and by employing a clock frequency proportional to absolute temperature (PTAT). The latter ensures accurate settling of the SC input stage at low temperatures, and reduces the effects of leakage currents at high temperatures.