We report on a lithographic mode of electrochemically triggered free radical polymerization. The polymerization is initiated by the reduction of an electrochemically active initiator. Hydrogel patterns can,be written by employing a small insulated counter electrode. The investigations show that the "pen" actually is a small oxygen bubble between the counter electrode and the sample surface. The spot size corresponds to the size of the bubble produced between the counter electrode and the substrate. The gas/liquid interface traps the growing chains and guides the growth of a gel layer at the bubble surface. Since bubbles can be created and controlled in many different ways, this mechanism constitutes an easy route for the formation of structured, surface-bound polymer layers.