A gas sensor includes zinc oxide nano-structures formed on a substrate, a plurality of metal islands coated on a surface of each zinc oxide nano-structure and separated from one another, a first electrode electrically connected to one end of each zinc oxide nano-structure through the substrate, a second electrode electrically connected to the other end of each zinc oxide nano-structure, and a current variation-measuring unit electrically connected to each of the first electrode and the second electrode so as to measure a variation in the amount of current flowing between the first electrode and the second electrode. In order to form the plurality of metal islands on the zinc oxide nano-structures, a solution of metal components of a metal material is coated on the surface of each zinc oxide nano-structure.