In the present study, UV light activated gas sensor was investigated for Al/Al2O3/p-Si and Al/TiO2/Al2O3/p-Si samplesby atomic layer deposition method (ALD). Generally, in order to obtain the sensing performance, traditional metal oxide semiconductor gas sensors are operated at 100-400 degrees C. However, this temperature range limits their applications to flammable gases, and causes high power consumption. It is important to note that sensing performance experiments should have been performed at room temperature. With the support of UV light, gas sensors do not need to be heated and they can work at room temperature easily. For this purpose, electrical measurements have been performed on sensing performance with and without UV irradiation for dedection of NO2 gas. With the help of UV irradition, we obtained good sensitivity at the room temperature for Al/TiO2/Al2O3/ p-Sistructure but under the same conditions no result was obtained for Al/Al2O3/p-Si structure. Without UV irradiation, there was no sensitivity for both.We observed that increasing of sensitivities at the room temperature show a direct effect of the light on the adsorbed oxygen ions. According to the relation of photocatalytic reaction and photoactivated gas sensing process, we concluded that TiO2 might be an acceptable sensor for detection of nitrogen dioxide (NO2) at room temperature under UV illumination. (C) 2014 Elsevier Ltd. All rights reserved.