A two-step thermolysis process is reported to grow highly crystalline and large-area molybdenum disulfide (MoS₂) thin layers on insulating substrates. The method involves the thermal decomposition of ammonium thiomolybdate in the presence of sulfur, followed by a second annealing step. The resulting MoS₂ layers exhibit excellent electrical performance, comparable to those obtained from mechanically exfoliated MoS₂. The process is simple, scalable, and applicable to other transition metal dichalcogenides. The MoS₂ films are transferable to various substrates, enabling the fabrication of layered composites. The synthesis involves a two-step process: first, the ammonium thiomolybdate solution is deposited on the substrate and annealed at 500°C in an Ar/H₂ atmosphere to form a MoS₂ precursor. Then, the sample is annealed at 1000°C in Ar or Ar/S to improve crystallinity. The resulting MoS₂ layers show high crystallinity, as evidenced by Raman, PL, XRD, TEM, and SAED analyses. The electron mobility of the MoS₂ transistors is up to 6 cm²/Vs, comparable to those from mechanically exfoliated MoS₂. The sulfur addition during the second annealing significantly enhances the crystallinity and electrical performance of the MoS₂ layers. The process is effective in reducing oxygen contamination, which can degrade the quality of the MoS₂ layers. The MoS₂ layers are uniform, continuous, and can be transferred to various substrates. The method provides a scalable and efficient way to produce high-quality MoS₂ thin layers for electronic applications.A two-step thermolysis process is reported to grow highly crystalline and large-area molybdenum disulfide (MoS₂) thin layers on insulating substrates. The method involves the thermal decomposition of ammonium thiomolybdate in the presence of sulfur, followed by a second annealing step. The resulting MoS₂ layers exhibit excellent electrical performance, comparable to those obtained from mechanically exfoliated MoS₂. The process is simple, scalable, and applicable to other transition metal dichalcogenides. The MoS₂ films are transferable to various substrates, enabling the fabrication of layered composites. The synthesis involves a two-step process: first, the ammonium thiomolybdate solution is deposited on the substrate and annealed at 500°C in an Ar/H₂ atmosphere to form a MoS₂ precursor. Then, the sample is annealed at 1000°C in Ar or Ar/S to improve crystallinity. The resulting MoS₂ layers show high crystallinity, as evidenced by Raman, PL, XRD, TEM, and SAED analyses. The electron mobility of the MoS₂ transistors is up to 6 cm²/Vs, comparable to those from mechanically exfoliated MoS₂. The sulfur addition during the second annealing significantly enhances the crystallinity and electrical performance of the MoS₂ layers. The process is effective in reducing oxygen contamination, which can degrade the quality of the MoS₂ layers. The MoS₂ layers are uniform, continuous, and can be transferred to various substrates. The method provides a scalable and efficient way to produce high-quality MoS₂ thin layers for electronic applications.