Wafer-scale, single-crystalline 2D semiconductors without grain boundaries and defects are needed for developing reliable next-generation integrated 2D electronics. Unfortunately, few literature reports exist on the growth of 2D semiconductors with single-crystalline structure at the wafer scale. It is shown that direct sulfurization of as-deposited epitaxial MoO2 films (especially, with thicknesses more than ≈5 nm) produces textured MoS2 films. This texture is inherited from the high density of defects present in the as-prepared epitaxial MoO2 film. In order to eliminate the texture of the converted MoS2 films, a new capping layer annealing process (CLAP) is introduced to improve the crystalline quality of as-deposited MoO2 films and minimize its defects. It is demonstrated that sulfurization of the CLAP-treated MoO2 films leads to the formation of single-crystalline MoS2 films, instead of textured films. It is shown that the single-crystalline MoS2 films exhibit field-effect mobility of 6.3 cm2 V−1 s−1, which is 15 times higher than that of textured MoS2. These results can be attributed to the smaller concentration of defects in the single-crystalline films.