An object of the present invention is to provide an etching liquid having a high silicon etch selectivity with respect to silicon-germanium and a high long term stability at a processing temperature, in surface processing during the production of various semiconductor devices, especially various silicon composite semiconductor devices containing silicon-germanium, and the problem is solved by a silicon etching liquid containing an alkaline compound, an aldehyde compound, and water, the aldehyde compound being a water-soluble aromatic aldehyde.