A silicon nitride etching composition effective to selectively etch a silicon nitride film contains an inorganic acid; a silicon-based compound; from 0.01 to 1 wt%, based on total weight of the etching composition, of an ammonium-based compound composed of ammonium acetic acid; and water. The silicon-based compound may be represented by Chemical Formula 1 below or Chemical Formula 2 below, (R1)3-Si-R2-Si-(R1)3  Chemical Formula 1, (R3)3-Si-R4-Si-(R3)3  Chemicl Formula 2. A method of etching a silicon nitride film includes providing the etching composition; and wet etching the silicon nitride film in the etching composition at an etching rate that is at least 200 times faster than a corresponding silicon oxide film.