Synthesis of atomically thin MoS 2 layers and its derivatives with large-area uniformity is an essential step to exploit the advanced properties of MoS2 for their possible applications in electronic and optoelectronic devices. In this work, a facile method is reported for the continuous synthesis of atomically thin MoS2 layers at wafer scale through thermolysis of a spin coated-ammonium tetrathiomolybdate film. The thickness and surface morphology of the sheets are characterized by atomic force microscopy. The optical properties are studied by UV-Visible absorption, Raman and photoluminescence spectroscopies. The compositional analysis of the layers is done by X-ray photoemission spectroscopy. The atomic structure and morphology of the grains in the polycrystalline MoS2 atomic layers are examined by high-angle annular dark-field scanning transmission electron microscopy. The electron mobilities of the sheets are evaluated using back-gate field-effect transistor configuration. The results indicate that this facile method is a promising approach to synthesize MoS2 thin films at the wafer scale and can also be applied to synthesis of WS2 and hybrid MoS2-WS2 thin layers.