Sensor response enhancement of ethanol sensors based on ZnO nanostructures decorated with gold nanoparticles (ZnO:AuNPs under dark condition), UV illumination (ZnO under UV illumination) and gold nanoparticles in combination with UV illumination (ZnO:AuNPs under UV illumination) was intensively investigated in the temperatures in the range of 25-150ºC. It was found that the sensor response of ZnO:AuNPs sensors under dark condition and ZnO sensors under UV illumination can be improved. Moreover, they can broadly respond to ethanol vapor at an operating temperature of 25-150ºC. The sensor based on ZnO:AuNPs under UV illumination exhibited the optimum sensor response to ethanol vapor at anoperating temperature of 25-150ºC. The sensor response enhancement mechanism can be divided in two main parts including sensor response enhancement due to addition of AuNPs and UV illumination. AuNPs added onto ZnO nanostructure really affect the chemical reaction change in the oxygen adsorption reaction resulting in a larger depletion layer width. Therefore, from the sensor response formula, it can enhance the sensor response to higher than that of ZnO nanostructure sensors. Finally, the sensor response enhancement due to UV illumination is explained by electron carriers being excited from band to band forming weakly bound oxygen ions. This produces a thinner depletion layer due to photo activation and they easily are removed from the ZnO surface resulting in high sensor response with lower resistance