To provide an etchant by which etching of silicon nitride is highly selectively performed without generating deposits after etching, in a step of removing silicon nitride from an electronic substrate having both a silicon dioxide layer and a silicon nitride layer.

The etchant for silicon nitride is used which contains, as essential components, a quaternary alkyl ammonium salt having a specific chemical structural formula, a basic compound, and an inorganic acid and/or an organic acid.