In etching processing of silicon, in particular anisotropic etching processing of silicon in a manufacturing step of MEMS parts, an etchant having a long life of etchant and an etching method are provided by suppressing a lowering of an etching rate at the time of warming which is characteristic of a hydroxylamine-containing etchant. A silicon etchant for anisotropically dissolving monocrystalline silicon therein, which is an alkaline aqueous solution containing (A) tetramethylammonium hydroxide, (B) hydroxylamine and (C) carbon dioxide (CO2) and/or a carbonic acid salt of tetramethylammonium and having a pH of 13 or more, and an etching method of silicon using this etchant are provided.
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