An etchant for patterning thin metal films by wet etching and in particular, an etchant for use in producing semiconductor devices, such as semiconductor elements and liquid-crystal display elements, is for application to a multilayer film having a first layer made of aluminum or an aluminum alloy having formed thereon a second layer made of aluminum or an aluminum alloy each containing at least one element selected from nitrogen, oxygen, silicon, and carbon, and has a phosphoric acid content of from 35 to 65% by weight and a nitric acid content of from 0.5 to 15% by weight; and an etching is performed using the etchant.