In order to judge the usability of novel semiconductors for field-effect transistors (FETs), fast tools for the assessment of relevant electrical transistor parameters are necessary. We discuss here the use of an ionic gel (IG) as gate material that allows the quick fabrication of, for example, graphene FETs. Our IG-FETs show excellent performance. For example, IG-gated FETs have a charge carrier mobility of 2000 cm2/Vs, which is 5 times larger than that previously reported in similar devices. Using cyclic voltammetry and electrochemical impedance spectroscopy in a detail previously not shown, we furthermore investigate the gating mechanism of as-fabricated CVD-grown graphene FETs and compare it with IG gated FETs based on regioregular poly(3-hexylthiophene) (rr-P3HT). Consistent with literature, we find that, while IG-based graphene transistors are gated electrostatically, IG-gated rr-P3HT transistors work via electrochemical doping. IGs and our presented electrical measurements will allow to judge the electrical quality and gating mechanism also of novel semiconductors. Finally, to the best of our knowledge, we are the first to show that with the aid of IGs, graphene can be functionalized electrochemically with a concomitant variation in conductance of more than an order of magnitude.

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