We report on the design and test of a low-voltage temperature sensor designed for MEMS power-harvesting systems. The core of the sensor is a bandgap voltage reference circuit operating with a supply voltage in the range of 1-1.5V. The prototype was fabricated on a conventional 0.5 mu m Silicon-on-Sapphire (SOS) process. The sensor design consumes 15 mu A of current at M The internal reference voltage is 550mV. The temperature sensor has a digital square wave output whose frequency is proportional to temperature. A linear model of the dependency of output frequency with temperature has a conversion factor of 1.6kHz/degrees C. The output is also independent of supply voltage in the range of 1-1.5V. We report measured results and targeted applications for the proposed circuit.