A thermal isolated micro-electro-mechanical system（ MEMS） gas mass flow sensor is developed. The thermal isolated cantilever structure is adopted for heating resistor

upstream and downstream resistors with 240 μm interval. The design key point of constant temperature difference circuit is analyzed

and system circuit is made.The curve of relationship between sensor output voltage and gas flow is measured

and accordingly sensor is calibrated. Test result shows that at flow range of 0

20 L / min

the sensor has fast response speed

high sensibility

smooth output signal

so the sensor is suitable for industrial and medical fields.