The present invention provides an ion conducting ceramic membrane selectively permeable to a gas, for instance oxygen and a method of treating such a membrane to improve permeation through the membrane. The membrane is formed by a mass of a substance through which ions of the gas migrate. The mass has two opposed surfaces where dissociation and ionization of the gas occurs and gas ions release electrons and recombine to form molecules of the gas, respectively. At least one of said two opposed surfaces is treated by a removal of surface material to produce surface irregularities of increased area and therefore an increase in total surface area of a treated surface to in turn increase permeation of the gas. Preferably, both surfaces of the membrane are treated by chemical etching techniques, although sand blasting and ion etching are other possible surface treatments in accordance with the present invention.