It is known that the Silicon nanowire (SiNW) arrays show remarkable antireflection characteristics, which makes them an important candidate to be used as an absorber in solar cells. These single crystal nanowires with desirable axial crystallographic orientations are prepared by a simple electrochemical etching process, which is based on a galvanic displacement reaction taking place between surface Si atoms and oxidizing metal ions such as Ag+. As a result of this process, a black colored surface is obtained which implies its excellent optical antireflection property. Therefore this material has a great potential to be used as an antireflection surface in photovoltaic applications.