Al/TiO2/p-Si and Al/TIO2/Al2O3/p-Si samples were prepared using the atomic layer deposition method (ALD) and their gas sensing properties were investigated. The electrical properties of the samples were studied using a two probe method in the temperature range 25-230 degrees C and at room temperature UV conditions. The TiO2/Al2O3 heterojunction sample exhibited an excellent gas sensing response to CO2 gas at room temperature and improved the effect of UV light irradiation. The results showed that heterostructures helped to improve the gas sensor properties, affected the sensing at room temperature and thus guided the design of photocatalysts. The TiO2/Al2O3 heterojunction prepared using this method can be used as a material for semiconductor gas sensors detecting poisonous gases like CO2 at room temperature with high sensitivity and selectivity.