The paper presents the results of experimental studies of GaAs nanowire growth on Si(111) substrate with Ga focused ion beam modified areas with different treatment doses. We observed a significant difference between the parameters of nanowires arrays formed on modified and unmodified areas. It is shown that changing the dose of Ga ions from 52 fC/µm2 to 1×104 fC/µm2 allows to form nanowire arrays with a different set of parameters in a single technological cycle with a high selectivity. The possibility of regulating of the NW length in the range of 1–6 µm, the density in the range of 0–7.8 µm-2, the diameter in the range of 28–95 nm and the normally oriented NWs in the range of 5–70 % by focused ion beam have been experimentally demonstrated. The change of modes and mechanisms of the catalytic centers formation and the initial stage of GaAs NWs growth were revealed.