A silica membrane was formed by chemical vapor deposition using tetraethylorthosilicate in macropores of an alpha-alumina tube or a gamma-alumina film coated on the alpha-alumina tube. The reactant was evacuated through the porous wall, and silica was deposited in the macropores at 600-700 degrees C. When the silica membrane was formed in a gamma-alumina film coated on the alpha-alumina tube, hydrogen permeance at a permeation temperature of 600 degrees C was 3 x 10(-7) mol m(-2) s(-1) Pa-1, which was one order of magnitude higher than that of a membrane formed directly on the alpha-alumina tube. H-2/N-2 selectivity determined from the permeance of each component was 100-1000. To separate hydrogen selectively from abundant steam, however, a higher permselectivity was required. The membrane formed in the gamma-alumina film at 650 degrees C showed a hydrogen permeance of 3 x 10(-8) mol m(-2) s(-1) Pa-1 and an H-2/H2O selectivity of 7.6 at 400 degrees C.