We present an Al₂O₃ dielectric layer on molybdenum disulfide (MoS₂), deposited using atomic layer deposition (ALD) with ozone/trimethylaluminum (TMA) and water/TMA as precursors. The results of atomic force microscopy and low-energy ion scattering spectroscopy show that using TMA and ozone as precursors leads to the formation of uniform Al₂O₃ layers, in contrast to the incomplete coverage we observe when using TMA/H₂O as precursors. Our Raman and X-ray photoelectron spectroscopy measurements indicate minimal variations in the MoS₂ structure after ozone treatment at 200 °C, suggesting its excellent chemical resistance to ozone.