The MEMS carbon monoxide gas sensor uses MEMS technology to make a micro-hot plate on a Si-based substrate, and the gas-sensing material used is a metal-oxide-semiconductor material with low conductivity in clean air. When the detected gas exists in the ambient air, the conductivity of the sensor changes. The higher the concentration of the gas, the higher the conductivity of the sensor. The change in conductivity can be converted into an output signal corresponding to the gas concentration using a simple circuit.