[en] A spin-coating method was applied to obtain thinner and smoother PEO/LiClO₄ polymer electrolyte films (EFs) with a lower level of crystallization than those obtained using a drop-casting method. When the applied frequency was as high as 10 kHz, the specific capacitance of such EFs with thicknesses of 1.5 μm was on the order of 1 μF∙cm⁻², a value larger than most of the previously reported results achieved from the same material. We then combined the thin EFs with two-dimensional (2D) materials to fabricate a MoS₂ transistor with a top gate right above the channel, defined by a shadow-mask method, and an inverter device. This transistor showed excellent static characteristics and the inverter device showed excellent switching performance at 100 Hz, which indicates a fast polarization response of the thin EFs. Such device architecture is suitable for future low power and flexible electronics based on 2D materials. .