The fabrication of silicon nanowire arrays by post-treatmant in alkali solution is proposed. First, vertically aligned silicon nanowire (SiNW) arrays are fabricated over large areas using an electroless etching (EE) method. Then the SiNW is dipped in the mixture of NaOH and IPA for 10, 30, 50, 60, 90 s, respectively. Each SiNW is separated from the bunched SiNW. Compared to the bunched SiNWs, the dispersed SiNW arrays could drastically suppress the optical reflection(<4%) over a wide range of 400~1000 nm spectral bandwidth. In additon, the mechanism of nanowires scattered by the alkaline solution is tentatively analysed which provides the reference for the optimization of the preparation and application of silicon nanowires arrays.