This thesis is focused on the fabrication of organic electrochemical transistors (OECTs) constituted by a silicon oxide substrate, gold source and drain electrodes and a poly-(3,4-ethylene-dioxythiophene):poly-(styrenesulfonate) (PEDOT:PSS) channel. Within the production process two improvements of the device properties were investigated: the addition of (3-glycidyloxypropyl)trimethoxysilane (GOPS) in the polymeric solution to enhance the adhesion on the substrate, and a post-deposition treatment of the original solution with sulfuric acid in order to improve the conductivity. These enhancements were combined with two different techniques for the PEDOT:PSS deposition: the spin coating and the ink-jet printing methods. After the fabrication, OECTs have been characterised in order to check if they worked properly, to evaluate their performances and finally to compare the devices, developed following the different fabrication approaches.