Large-area GaAs nanowires are fabricated using SiO2 nanoparticles as the etching mask. SiO2 nanoparticle monolayer is spin coated on the GaAs substrate. To obtain a uniform monolayer of SiO2 nanoparticles across the substrate, raised temperature, adequate solution concentration, and the substrate treated with a solvent for interface activation are required. With the monolayer of SiO2 nanoparticles as the etching mask, the GaAs substrate is etched by induced-coupled plasma reactive ion etcher (ICP-RIE) to form GaAs nanowires with a high aspect ratio. The diameter and length of GaAs nanowires are 70 nm and 1.2 mu m, respectively. The diameter and length of GaAs nanowires can be controlled by the size of SiO2 nanoparticles and etching time of ICP-RIE.