The present invention provides a gas sensor, including: a sensor substrate provided with an electrode; and a thin layer of sensor material formed by spraying a solution in which metal oxide nanoparticles are dispersed onto the sensor substrate. The gas sensor is advantageous in that a sensor material is formed into a porous thin layer containing metal oxide nanoparticles having a large specific surface area, thus realizing high sensitivity on the ppb scale and a high reaction rate. Further, the gas sensor is advantageous in that it can be manufactured at room temperature, and the thickness of a sensor material can be easily adjusted by adjusting the spray time, so that a thin gas sensor or a thick gas sensor can be easily manufactured.