Ionic liquids have attracted significant interest in a wide variety of applications including electronic, electrochemical, and energy storage devices. This thesis investigates the use of ionic liquid-based polymer electrolytes (ion gels) as a gate insulator material for thin-film transistors. The first objective of thesis is to study the electrical properties of ion gels systematically to understand how the ion gels work as a capacitor to accumulate charge carriers in a semiconductor channel. Accordingly, electrical properties including specific capacitance, resistance and conductivity of ion gels were investigated as a function of film geometry (thickness and area) and temperature. This research also aims to develop new routes for incorporating an ion gel layer on a device to provide diversity and universality in ion gel processing. The first effort was devoted to prepare a smooth and uniform layer of ion gel by spin casting. Typical thicknesses of spin-coated ion gels were 1~20 m. Alternatively, transfer printing using an elastomeric stamp was utilized to prepare all-printed (semiconductor, ion gel dielectric, and gate electrode) thin-film transistors. For the last, mechanically free-standing ion gels that can be cut by hand and laminated on a layer of semiconductor using tweezers were developed for thin-film transistors. This `cut and stick' strategy facilitates convenient fabrication of transistors on a variety of semiconductor materials. Overall, these new processes provide reliable routes to employ ion gels on electrical and electrochemical devices.