The sol-gel method was applied to the fabrication of amorphous silica membranes for use in hydrogen separation at high temperatures. The effects of fabrication temperature on the hydrogen permeation properties and the hydrothermal stability of amorphous silica membranes were evaluated. A thin continuous silica separation layer (thickness=<300nm) was successfully formed on the top of a deposited colloidal silica layer in a porous glass support. After heat treatment at 800 degrees C for an amorphous silica membrane fabricated at 550 degrees C, however, it was quite difficult to distinguish the active separation layer from the deposited colloidal silica layer in a porous glass support, due to the adhesion of colloidal silica caused by sintering at high temperatures. The amorphous silica membranes fabricated at 700 degrees C were relatively stable under steam atmosphere (500 degrees C, steam=70kPa), and showed steady He and H2 permeance values of 4.0x10-7 and 1.0x 10-7molm-2s-1Pa-1 with H2/CH4 and H2/H2O permeance ratios of similar to 110 and 22, respectively. The permeance ratios of H2/H2O for membranes fired at 700 degrees C increased drastically over the range of He/H2 permeance ratios by factors of similar to 3-4, and showed a value of similar to 30, which was higher than those fired at 500 degrees C. Less permeation of water vapor through amorphous silica membranes fabricated at high temperatures can be ascribed to the dense amorphous silica structure caused by the condensation reaction of silanol groups.