Abstract This work consists in elaborating a gas sensor based on porous silicon and a polypyrrole obtained by covalent grafting and studying its answer in different environments. At first, we were interested in the formation of the nanoporous layers by cyclovoltammetric (CV) in a hydrofluoric acid solution followed by an electrochemical grafting of the polypyrrole (PPy) on the porous silicon and oxide porous silicon surfaces. The various interfaces were characterized using different techniques such as Fourier transform infrared spectroscopy (FT-IR), energy dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM). Finally, a series of electric characterizations to study the answer of the structures in the contact of the carbon dioxide was achieved.