A gas sensor with a gas permeable region is disclosed. In an embodiment a gas sensor includes a dielectric membrane formed on a semiconductor substrate having a cavity portion, a heater located within or over the dielectric membrane, a material for sensing a gas, wherein the material is located on one side of the dielectric membrane, a support structure located near the material, a gas permeable membrane coupled to the support structure so as to protect the material, wherein the semiconductor substrate forms the support structure.