Etchant compositions for selective etching of silicon nitride in the presence of silicon oxide and polysilicon are provided. The etchant compositions may achieve passivation of at least one of silicon oxide, polysilicon, or any combination thereof, while selectively etching silicon nitride, in a single step by applying the etchant composition to a substrate. The etchant compositions may comprise at least 60% by weight of phosphoric acid based on a total weight of the etchant composition; at least 1% by weight of water based on the total weight of the etchant composition; and no greater than 2% by weight of a metal oxidizer based on the total weight of the etchant composition.