A sensor device configured to determine an air flow rate, the sensor device comprises: a cavity formed in an Si substrate, a first insulating film covering the cavity, a second insulating film covering the first insulating film, a first heating unit formed on the first insulating film, and a second heating unit formed on the second insulating film, upstream temperature sensors (9a, 9b) which are configured to measure a first temperature which is a temperature of the air on the upstream side of the heating unit, downstream temperature sensors (11a, 11b) which are configured to measure a second temperature which is a temperature of the air on the downstream side of the heating unit, wherein on the first insulating film a first upstream temperature sensor and a first downstream temperature sensor are formed from a first polycrystal silicon film and wherein on the second insulating film a second upstream temperature sensor and a second downstream temperature sensor are formed from a second polycrystal silicon film, wherein the second insulating film is formed on the first polycrystal silicon element and on the second polycrystal silicon element a third insulating film is formed, wherein the first polycrystal silicon film is patterned into a plurality of first polycrystal elements forming the first heating unit, the first upstream temperature sensor and the first downstream temperature sensor, wherein the second polycrystal silicon film is patterned into a plurality of second polycrystal elements forming the second heating unit, the second upstream temperature sensor and the second downstream temperature sensor, wherein the plurality of first polycrystal silicon elements are doped with a first impurity and the plurality of second polycrystal silicon elements are doped with a second impurity, which is different to the first impurity, and wherein the sensor device is further configured to determine a flow rate of the air based on a difference between the first temperature and the second temperature based on changing a resistance value of the polycrystal silicon elements. a cavity formed in an Si substrate, a first insulating film covering the cavity, a second insulating film covering the first insulating film, a first heating unit formed on the first insulating film, and a second heating unit formed on the second insulating film, upstream temperature sensors (9a, 9b) which are configured to measure a first temperature which is a temperature of the air on the upstream side of the heating unit, downstream temperature sensors (11a, 11b) which are configured to measure a second temperature which is a temperature of the air on the downstream side of the heating unit, wherein on the first insulating film a first upstream temperature sensor and a first downstream temperature sensor are formed from a first polycrystal silicon film and wherein on the second insulating film a second upstream temperature sensor and a second downstream temperature sensor are formed from a second polycrystal silicon film, wherein the second insulating film is formed on the first polycrystal silicon element and on the second polycrystal silicon element a third insulating film is formed, wherein the first polycrystal silicon film is patterned into a plurality of first polycrystal elements forming the first heating unit, the first upstream temperature sensor and the first downstream temperature sensor, wherein the second polycrystal silicon film is patterned into a plurality of second polycrystal elements forming the second heating unit, the second upstream temperature sensor and the second downstream temperature sensor, wherein the plurality of first polycrystal silicon elements are doped with a first impurity and the plurality of second polycrystal silicon elements are doped with a second impurity, which is different to the first impurity, and wherein the sensor device is further configured to determine a flow rate of the air based on a difference between the first temperature and the second temperature based on changing a resistance value of the polycrystal silicon elements.