A dual-frequency technique for electronically measuring high-order derivatives by frequency mixing is described. The technique utilizes an ac modulation at two distinct but synchronous frequencies to produce a derivative signal at a useful difference frequency which is unique to the order of the derivative being measured. By appropriate selection of the frequencies, significant experimental advantages are obtained compared to the conventional method in which derivatives are sensed at harmonics of a single frequency. The technique is illustrated with a practical measurement of the second derivative of the electrical characteristic of a silicon rectifier diode.