Electrolyte-gated organic field-effect transistors (EGOFETs) are the transducer of choice for many ion- and biosensor applications. Due to the formation of an electric double layer at the electrolyte/organic semiconductor interface, they exhibit a very high capacitance allowing for low-voltage and therefore the necessary stable operation in aqueous environment. We show that also using poly(3-hexylthiophene) (P3HT) based EGOFET devices, one can overcome oxygen and water induced degradation processes, normally observed for this polymer, when operating the device in the right gate potential window, avoiding electrochemical processes at the polymer water interface. Moreover, the use of a polymeric blend of P3HT with poly(methyl methacrylate) (PMMA) as the active layers showed improve device stability, as it was tested. We also tested the response of the device as function of the distance between the active EGOFET and the gate wire, aiming to use the device in different sensor applications. Based on the transfer curves of the devices, it was found that the choice of a proper operational window is the most critical parameter and seems to limit both P3HT and P3HT:PMMA systems to the same gate potential which seem to be more important than choice of the semiconductor material as such. Moreover, we could show that the EGOFET device performance is almost independent of the distance between the gate wire and the device pixel within the correct gate potential window.