The paper presents a method for growing large-area, highly crystalline MoS₂ thin layers on insulating substrates through a two-step thermolysis process. The first step involves dip-coating a solution of ammonium thiomolybdate (NH₄)₂MoS₄ onto an insulating substrate, followed by slow pulling to form a thin film. The second step includes two annealing processes: a first annealing at 500°C in a gas mixture of Ar and H₂ to remove residual solvents and by-products, and a second annealing at 1000°C in pure Ar or a mixture of Ar and sulfur to improve crystallinity. The addition of sulfur during the second annealing significantly enhances the crystallinity and electrical performance of the MoS₂ layers. Spectroscopic and microscopic analyses, including Raman, photoluminescence (PL), X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED), confirm the high crystallinity and quality of the MoS₂ layers. Field-effect transistors (FETs) fabricated using these MoS₂ layers exhibit excellent on/off current ratios and electron mobilities, comparable to those of micromechanically exfoliated MoS₂ thin sheets. The synthetic approach is simple, scalable, and applicable to other transition metal dichalcogenides, making it a promising method for producing high-quality MoS₂ thin layers for electronic applications.The paper presents a method for growing large-area, highly crystalline MoS₂ thin layers on insulating substrates through a two-step thermolysis process. The first step involves dip-coating a solution of ammonium thiomolybdate (NH₄)₂MoS₄ onto an insulating substrate, followed by slow pulling to form a thin film. The second step includes two annealing processes: a first annealing at 500°C in a gas mixture of Ar and H₂ to remove residual solvents and by-products, and a second annealing at 1000°C in pure Ar or a mixture of Ar and sulfur to improve crystallinity. The addition of sulfur during the second annealing significantly enhances the crystallinity and electrical performance of the MoS₂ layers. Spectroscopic and microscopic analyses, including Raman, photoluminescence (PL), X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED), confirm the high crystallinity and quality of the MoS₂ layers. Field-effect transistors (FETs) fabricated using these MoS₂ layers exhibit excellent on/off current ratios and electron mobilities, comparable to those of micromechanically exfoliated MoS₂ thin sheets. The synthetic approach is simple, scalable, and applicable to other transition metal dichalcogenides, making it a promising method for producing high-quality MoS₂ thin layers for electronic applications.