Complete descriptions of the calculations and experiments for electrostatically controlled double-quantum-wire electron interferometers are presented. The interferometers are constituted by straight, asymmetric double-quantum-wire structures and triple Schottky gates. The electron wave function in the double-quantum-wire structure is electrostatically controlled by the Schottky gates so that an Aharonov–Bohm-type or a directional-coupler-type interferometer is effectively formed. To show that the interferometers really work, and to obtain structural parameters for a large amplitude of oscillations, numerical calculations of the electron wave propagation were performed assuming two-dimensional electron gas, by use of a scattering matrix formalism obtained by the mode-matching method. The calculated source-drain transmission of the electron wave shows oscillations with almost 100% modulation depth if the potential barrier between both quantum wires and the length between the main (central) gate and the sub- (side) gates are properly designed. On the basis of these calculations, Al0.3Ga0.7As/GaAs modulation-doped double-quantum-well structures were fabricated by standard molecular-beam epitaxy. The ballistic lengths of the two-dimensional electron gas at 4.2 K, determined by Hall measurement, were about 5 μm for the upper well and about 0.6 μm for the lower well. The interferometers with lengths of about 0.9 μm were fabricated from these quantum-well structures using electron-beam lithography, reactive-ion-beam etching, and liftoff techniques. The fabricated interferometers were refrigerated at 1.8 K, and source-drain resistance was measured at various subgate bias conditions. When the subgate voltages were controlled such that the interferometers are formed, the oscillations of the resistance were observed as a function of the main-gate voltage. Also, the oscillations in the magnetoresistance were observed with magnetic flux penetrating the area surrounded by the split wave functions. The oscillation amplitudes were about 4% for both cases. Finally, to show that the proposed structure is certainly easy to fabricate, the interferometer was fabricated without electron-beam lithographic techniques, in which the oscillations in the resistance were also observed at 1.8 K.