The disordering and compositional change of the InGaAs/InP superlattice by the Ga ion beam was investigated, and using the effect, quantum wires were fabricated by focused Ga ion beam. The analysis of Raman scattering shows that in the implanted region intermixing, i.e., alloying takes place in such a way that the intermixed In1−xGaxAsyP1−yalloy has the compositions of alloy with the lattice constant nearly equal to that of InP, although at higher doses the compositionsxandybecome smaller due to larger interdiffusion. Focused Ga ion beam of 100 kV was irradiated in lines onto InP (350 Å)/InGaAs (50 Å)/InP (500 Å) single quantum well at doses of 1×1013–1×1014cm−2. Implanted samples were annealed at 650–670 °C for 60 min. The photoluminescence measurements at 30 K for wires with various widths show that with decreasing wire width the luminescence peak energy increases nearly following the change of the quantum levels in the potential well calculated by taking into account lateral straggling of implanted Ga ions. The implanted and alloyed regions are confirmed to act as potential barriers by which carriers are confined.