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Detection of pollutant, toxic, refining, combustible and process gases is important for system and process control,safety monitoring and envi-ronmental protection. Gas sensors based on Metal semiconductor materials (MOS) offerconsiderable advantages in comparison to other gas sensing methods. Semiconductor sensors are inexpensive to pro-duce,easy to miniaturize, rugged, reliable and can be designed to operate over a range of conditions in-cluding high temperatures.Semiconductor sensors can be produced in arrays to allow sensing of multi-ple species simultaneously and with advances insensitivity; limits are approaching part-per-million (ppm) levels for some species (T. A. Miller and all, 2006).The gas sensors based on MOS thick films such as SnO2, TiO2, WO3, V2O5, ZnO, Fe2O3, and In2O3 have been used to detectvarious gases such as ethanol, LPG, CO2 and CO gases etc (Supab Choopun and all, 2012).In the present paper, a gas sensing device based on Vanadium oxide thin films (V2O5)/ Porous Si (PS) / Si structure hasbeen used to detect CO2 gas and Ethanol at different concentration. Amorphous and crystalline vanadium pentoxide (V2O5)thin films were grown onto moncristalline silicon and porous silicon substrates using the Dip-coating method. The obtainedfilms were characterized by SEM and FTIR spectroscopy. The results show that the sensitivity of the structure increases withincreasing bias potential and concentration of CO2 and Ethanol vapors.