Abstract: Proposed is an aqueous developer solution for an alkali-developable photoresist composition which contains, besides a water-soluble organic basic compound such as tetramethyl ammonium hydroxide and an anionic or non-ionic surface active agent as conventional ingredients in the prior art developwer solutions, an inorganic ammonium salt such as ammonium sulfate, ammonium phosphates and ammonium borates in a limited amount. By virtue of this unique additive, the developer solution is advantageous in respect of the absence of any scums on the patterned resist layer obtained by the development treatment therewith as well as quite good orthogonality in the cross sectional profile of line-patterned resist layer in addition to the greatly improved latitude in the light exposure dose and range of focusing depth in the light-exposure process of the resist layer with ultraviolet light.