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The high capacitance from an electrolyte dielectric layer used in a thin film transistor architecture results in the development of electrolyte-gated organic field effect transistors (EGOFETs), which are able to operate at lower voltages compared with the commonly organic field effect transistors. When ions diffuse into the semiconductor, changing its conductive properties, the resulting devices are named organic electrochemical transistors (OECTs). In this case, an increase in channel conductivity occurs due to ionic doping. Depending on the gate voltage range operation, it is possible to obtain a de-doping process, suitable for achieving a low off-current. In this work, a simple and easy method is proposed based on an additional dielectric layer deposition of poly(methyl methacrylate) at the electrolyte dielectric/semiconductor interface, which provides: (i) good efficiency to block the diffusion of anions into the channel, resulting in an EGOFET for a gate voltage range up to − 0.6 V and (ii) an improvement in the on–off ratio in approximately three orders of magnitude for OECTs due to the low off-current obtained without promoting ionic de-doping in the channel, for a gate voltage range up to − 1.1 V. Both modes of operation were obtained in the same transistor structure. In addition, parameters such as field effect mobility, on–off ratio, and threshold voltage were also estimated for different transistor structures and gate voltage ranges. [ABSTRACT FROM AUTHOR]