Fabrication of large-area and uniform semiconducting thin films of two-dimensional (2D) materials is paramount for the full exploitation of their atomic thicknesses and smooth surfaces in integrated circuits.In addition to elaborate vapor-based synthesis techniques for the wafer-scale growth of 2D films,solution-based approaches for high-quality thin films from the liquid dispersions of 2D flakes,despite underdeveloped,are alternative cost-effective tactics.Here,we present layer-by-layer (LbL) assembly as an effective approach to obtaining scalable semiconducting films of molybdenum disulfide (MoS2) for field-effect transistors (FETs).LbL assembly is achieved by coordinating electrochemically exfoliated MoS2 with cationic poly (diallyldimethylammonium chloride) (PDDA)through electrostatic interactions.The PDDA/MoS2 percolating nanofilms show controlled and self-limited growth on a variety of substrates,and are easily patterned through lift-off processes.Ion gel gated FETs are fabricated on these MoS2 nanofilms,and they show mobilities of 9.8 cm2·V-1·s-1,on/off ratios of 2.1 × 105 with operating voltages less than 2 V.The annealing temperature in the fabrication process can be as low as 200 ℃,thereby permitting the fabrication of flexible FETs on polyethylene terephthalate substrates.The LbL assembly technique holds great promise for the large-scale fabrication of flexible electronics based on solution-processed 2D semiconductors.