We present a theoretical study of a recently proposed class of quantum interference transistors that utilize quantum interference effects in ultrasmall semiconductorTstructures. Our analysis reveals that the attractive features of these transistors are the very low power‐delay product and multifunctionality; whereas the major drawbacks are extreme sensitivity of the device characteristics to slight structural variations, low gain, and low extrinsic switching speed in digital circuits caused by a large resistance‐capacitance (RC) time constant arising from an inherently low current‐carrying capability. The low switching speed of the transistors can however be improved dramatically by switching the device optically rather than electronically, using virtual charge polarization caused by optical excitation. This mode of switching (which is possible because of the small value of the threshold voltage) eliminates theRCtime constant limitation on the switching time and results in an ultrafast optoelectronic switch.