Layer-by-layer assembled 2D montmorillonite nanosheets are shown to be high-performance, solution-processed dielectrics. These scalable and spatially uniform sub-10 nm thick dielectrics yield high areal capacitances of approximate to 600 nF cm(-2) and low leakage currents down to 6 x 10(-9) A cm(-2) that enable low voltage operation of p-type semiconducting single-walled carbon nanotube and ntype indium gallium zinc oxide fi eld-effect transistors.