A highly digital temperature sensor, based on the thermal diffusivity of silicon, for thermal management applications has been reported. Recently, Thermal-Diffusivity based temperature sensors have undergone a radical change from an analog-based readout architecture to a more digital VCO-based one. However the more digital approach led to significantly worse performance, i.e. accuracy and resolution. The proposed sensor uses the same digital approach but achieves much better performance. The sensor achieves an inaccuracy of ±2.9 °C (3?) from -35 °C to 125 °C with no trimming and ±1.2 °C (3?) after a single-point trim, while achieving a resolution of 0.47 °C (rms) at 1 kSa/s. Its compact area (2800 ?m²) is enabled by the adoption of a VCO-based phase-domain ADC. Since 53% of the sensor area is occupied by digital circuitry, the sensor can be easily ported to more advanced CMOS technologies with further area reduction, which makes it well suited for thermal monitoring in microprocessors and other systems-on-chip.