A temperature sensor cascading a reflective Fabry-Perot (FP) etalon with a microring resonator is proposed. This temperature sensor is composed of a fiber mirror, an FP etalon, and a microring resonator. The intensity interrogation method is employed, and both the simulation calculation and experimental verification results show that the proposed temperature sensor offers high sensitivity and a low detection limit. A combination of a broadband light source and a filter is used as the input light source for the experiment. The reflective FP etalon plays the role of a filter, and the temperature sensing element is the microring resonator. The sensitivity of the proposed temperature sensor yielded by the simulation calculation is 2.1406 dB/℃. The experimental results show that the sensitivity of the temperature sensor is 1.9434 dB/℃, and its detection limit is 0.01 ℃.