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A switching controlled thermal mass air flow sensor with low electric power dissipation has been developed. This thermal mass air flow sensor is operated by the well-known constant temperature method. In addition to the conventional bridge circuit, the new thermal mass air flow sensor provides a filter and a pulse width-modulation inverter (PWM), which turns the power transistor on and off. Therefore, electric power loss is reduced, so that it is possible to greatly reduce the heat sink of the power transistor. In this paper, we discuss the improved design and performance characteristics of the switching control circuit in comparison with a conventional circuit, as shown in Figure 1. We use a platinum wire of 70 μm diameter for the heating element.