A model for image formation in the Ag2Se/GexSe1-x resist systems had been proposed by Tai et al.1 The first step of the process consists of forming a thin latent image of photodoped Ag in the top layer of the GexSel-x film. This Ag doped layer then serves as a mask for the anisotropic wet chemical etching of the undoped GexSel-x structure with a bicomponent etchant. Anisotropic chemical etching results from an unusual, interlocked, phase-separated columnar structure of the GexSel-x film. The formation of such phase-separated columnar structures depends on the composition of the Germanium-Selenium film. We examine here the dependence of film microstructure on film composition and describe the relationship bewtween etching characteristics and the concentration ratios of a bicomponent developer.