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We report a systematic study of the etching of MoS₂ crystals by using XeF₂ as a gaseous reactant. By controlling the etching process, monolayer MoS₂ with uniform morphology can be obtained. The Raman and photoluminescence spectra of the resulting material were similar to those of exfoliated MoS₂. Utilizing this strategy, different patterns such as a Hall bar structure and a hexagonal array can be realized. Furthermore, the etching mechanism was studied by introducing graphene as an etching mask. We believe our technique opens an easy and controllable way of etching MoS₂, which can be used to fabricate complex nanostructures, such as nanoribbons, quantum dots, and transistor structures. This etching process using XeF₂ can also be extended to other interesting two-dimensional crystals.