A method of fabricating a deflection aperture array used in an electron beam exposure apparatus and a wet etching method and apparatus for fabricating the deflection aperture array are disclosed. In wet etching an aperture array substrate, a jig is used for holding the substrate in such a manner that only a portion of the reverse side to be etched is exposed to an etching solution so that the surface protective film can be removed before wet etching. According to the wet etching method, a gas is introduced into or discharged from an enclosed spacing facing a non-etched surface thereby to adjust the internal pressure of the enclosed spacing. The internal pressure of the enclosed spacing is thus detected and held at a predetermined value in accordance with the detected pressure.