A low power smart temperature sensor followed by an SC amplifier, buffer stage and a 12bit Successive-Approximation analogue-digital converter (ADC) for autonomous multi-sensor systems is presented. The proposed design is accurate within 0.1C over the temperature range of 55°C to 125°C. A PTAT source like the one presented in [1] was used as a high accuracy temperature sensor. The read-out enables a differential reading of the reference and actual temperature. The succeeding ADC digitizes the output with a bit-clock of 50-kHz. The power consumption with a 1.2V supply is 0.1μW. The ADC has a Figure-of-Merit of 66 fJ/conversion-step. The whole system is implemented in the NXP CMOS 0.14m technology. The die area is 0.27 mmp2 and the whole system consumes less than 16μW.