Here we present a straightforward and versatile 3D printing technique, referred to as gel-pen, for direct writing of organic semiconductor microelectronic devices (OSMDs). This approach is based on in-situ electrochemical deposition of the meniscus provided by a hydrogel cartridge at the electrode interface. Fabrication and characterization of OSMDs with arbitrary shapes and geometries have been successfully demonstrated via gel-pen 3D printer.