The growth of InP islands on a planar focused-ion-beam (FIB)-modified (001) GaAs substrate was investigated in a hydride vapor phase epitaxy system. InP grew selectively on the FIB-implanted lines, forming continuous stripes, whereas isolated islands were observed outside the implanted area. The impact of the III/V ratio, crystallographic orientation of implanted lines, and implantation dose was explored. The choice of suitable growth conditions makes it possible to obtain continuous InP wires aligned in all possible directions. The results of this work could be used for the fabrication of future optoelectronic integrated circuits, which would include nanoscale structures, e.g., quantum-wire optical devices with GaAs electronic circuits.