The present invention provides an etching solution in which a change in the composition due to the evaporation of the chemical solution or the like is small, thus reducing the frequency with which the chemical solution must be replaced, and in which the time-dependent change in etch rate is also small, thus allowing uniform etching of a silicon oxide film. Specifically, the present invention relates to an etching solution, a process of producing the same, and an etching process using the same, in which the etching solution includes hydrofluoric acid (a), ammonium fluoride (b), and salt (c) formed between hydrogen fluoride and a base having a boiling point higher than that of ammonia; the concentration of ammonium fluoride (b) is not higher than 8.2 mol/kg, and the total amount of ammonium fluoride (b) and salt (c) formed between hydrogen fluoride and a base having a boiling point higher than that of ammonia is not less than 9.5 mol/kg.