In this work,porous silicon (PSi) based gas sensor of structure (AL/nPSi/n-Si/AL) at different morphologies was prepared on the n-type silicon substrate using IR illuminated source of wavelength (810nm). The morphological and gas sensing properties of the sample were studied, under various etching time (5-20min). The current density –voltage characteristic at temperaturefrom 25 to 150 °C of the sensor,which was sensitivity analysis based on the silicon nano size, porosity, layer thickness, and effective dielectric constant of the PSi layer.The SEM image of the PSi layer showed the formation single layer structure pore –like the cylindrical and rectangular pore shape. The porous layer after etching time (5-10min) and double of mud _like for 20min produced different dimensions with randomly distributed as an upper layer and pore _like structure as a lower layer. The current density–voltage analysis confirms that higher temperatures with the presence of CO2 gas lead to sharply increase the sensitivity with the current and voltage. Overall, the improvement that appeared on the double porous layer sensitivity due to the higher value of the surface area.