A precision temperature sensing system includes a heater and a sensing element disposed on a semiconductor substrate. A power source drives the heater on a periodic basis according to a received clock signal. The sensing element senses the heat emitted by the heater and diffused through the semiconductor substrate. Processing circuitry coupled to the sensing element adjusts a phase of the periodic heater driving signal based on the heat sensed by the sensing element. The processing circuitry determines a temperature based on a thermal diffusivity (TD) of the semiconductor substrate, the adjusted value of the phase, and a known distance between the heater and the sensing element. A second temperature sensor can be disposed on the same substrate as the precision temperature sensing system, and calibrated based on temperature measurements obtained while applying a reference frequency signal to the precision sensing system.