A composition for etching a silicon oxide layer, a method of etching a semiconductor device, and a composition for etching a semiconductor device including a silicon oxide layer and a nitride layer including hydrogen fluoride, an anionic polymer, and deionized water, wherein the anionic polymer is included in an amount of about 0.001 to about 2 wt % based on the total weight of the composition for etching a silicon oxide layer, and an etch selectivity of the silicon oxide layer with respect to a nitride layer is about 80 or greater.