Disclosed is a semiconductor flow detector, comprising a semiconductor flow detecting element including a heating element and a pair of temperature-measuring elements formed in the substrate, a detecting element for detecting the temperature of the fluid under measurement, a first driving circuit for heating the heating element to keep the temperature of the semiconductor flow detecting element higher by a prescribed level than the temperature of the fluid under measurement, an electric power detection circuit for detecting the electric power flowing through the heating element so as to generate an electric power detection signal, a second driving circuit for driving the pair of the temperature-measuring elements, a temperature difference detecting circuit for detecting the temperature difference between the pair of the temperature-measuring elements so as to generate a temperature difference signal, and an arithmetic circuit for performing prescribed arithmetic operations among the electric power detection signal and the temperature difference signal so as to determine the flow rate and flowing direction of the fluid.