Resistor elements are formed by doping impurity into a single crystal film formed on a substrate such as a silicon-on-insulator substrate. A semiconductor device having such resistor elements is used as a detector for detecting an amount of airflow, for example. The impurity density in the single crystal silicon is made lower than 1×1020/cm3 to suppress a resistance change by aging especially at a temperature higher than 310° C. To obtain a high temperature coefficient of the resistor element as well as a low resistance change by aging, the impurity density is set in a range from 4×1019/cm3 to 1×1020/cm3, and more preferably in a range from 7×1019/cm3 to 1×1020/cm3. As the impurity, N-type impurity such as phosphorus or P-type impurity such as boron may be used. It is preferable to use the impurity having a low diffusion coefficient to attain a low resistance change by aging.