Three-dimensional arrays of vertically stacked sidewall quantum wires are fabricated by molecular beam epitaxy on GaAs(311)Asubstrates patterned with 500-nm-pitch gratings. The cathodoluminescence spectra at low temperature are dominated by the emission from the quantum wires with narrow linewidth accompanied by a very weak emission from the connecting thin quantum wells due to localization of excitons at random interface fluctuations. When the carriers in the quantum well become delocalized at elevated temperature, only the strong emission from the quantum-wire array is observed revealing perfect carrier capture into the quantum wires without detectable thermal repopulation of the quantum well up to room temperature. Thus, unpreceded device quality of this quantum-wire structure is demonstrated. ©1998 American Institute of Physics.