Highly oriented gallium arsenide (GaAs) nanowires are grown on GaAs (100), (110) and (111) substrates by molecularbeam epitaxy using vapor-liquid-solid growth. The preferred growth direction of the nanowires is <111>. GaAs nanowire arrays are grown using a number of approaches such as nanochannel alumina template, gold colloid, and
patterns fabricated using focused ion beam. Large interwire separation in the range of submicron can be obtained using the later two methods, which is required for applications in photonic devices such as photonic crystals.