Abstract We have developed a new method to directly synthesize GaAs quantum-well-wire (QWW) structures by molecular beam epitaxy. The method is based on the in-situ formation of a periodic array of nanometer scale macrosteps or facets by breaking up a surface with high surface energy into facets corresponding to planes with lower energy. RHEED directly reveals the formation of such macrosteps on the GaAs(311)A surface. The existence of GaAs QWW structures is confirmed by a pronounced anisotropy of the electronic properties. PL and PLE measurements reveal distinct energy shifts of the excitonic resonances and a strong polarization anisotropy. Confinement energies up to 90 meV are determined from the appearance of phonon related lines in the PLE spectra. The extremely high integrated luminescence intensity does not degrade with temperature up to 400 K. A strong anisotropy in conductivity is observed in modulation-doped quantum wires. These new directly synthesized QWW structures are important not only for fundamental research but also for applications in optoelectronic devices.