Abstract: An electrochemical sensor is provided on a substrate whereby a precious metal layer is arranged in an inner region under an electrolyte layer that is surrounded by a polyimide structure. A hydrophobic layer is surrounded by an outer polyimide structure and further is located on top of the electrolyte layer and extends laterally beyond the electrolyte layer. A lead for electrical connection of the precious metal layer extends under the hydrophobic layer laterally from the electrolyte layer is sealed from the hydrophobic layer by a protective layer. The protective layer prevents the penetration of analysis fluid into the gap between the hydrophobic layer and the surrounding polyimide structure into the inner region of the sensor. The material of the protective layer is preferably a double layer of PECVD oxide and PECVD nitride.