Photonic crystals (PhC) have a unique band structure that opens up a lot of possibilities in terms of manipulating electromagnetic waves. Lately a lot of research has been done in possible applications of photonic crystals as gas sensors. In this work we are dedicated in fabricating and then characterizing the optical response of photonic crystals based in macroporous silicon. The principal goal of this study is to fabricate photonic crystals that work as selective emitters, taking advantage of the fact that, when heated, they emit radiation at the designed wavelengths. In concrete, the technology used in our laboratories allows us to work at the mid-IR range (2 - 30 ?m) where most of the major gases -such as CO2, CO, methane, nitrous oxide, etc. have their principal absorption band. For the fabrication part, the electrochemical etching technique is used in order to create the pores through the silicon substrate. To achieve the desired results several voltage-current profiles have been generated and characterized both in transmission and emission. After several trials to optimize the photonic band, a 700 nm square lattice of macroporous structure was fabricated by electrochemical etching, creating a photonic gap centered at 4.25 ?m, accordingly to the absorption band of the CO2. After the required results are obtained we proceed to do the gas measurement, in particular, CO2. By introducing the gas into the structure, the optical response changes accordingly to the volume of gas introduced, that way detecting the concentration of the gaseous substance.