Reference electrode

A planar reference electrode for chemical sensors which can be supplied with a test liquid and a calibration liquid, has the following components: a pick-up electrode located on a planar substrate, a layer which covers the substrate in the vicinity of the pick-up electrode and is made of a patterned polymer having at least one groove which acts as a diffusion channel and extends in a lateral direction from the pick-up electrode to a zone which comes into contact with the test liquid or calibration liquid, respectively, to be supplied to the chemical sensor, the diffusion in the diffusion channel being determined by the geometry of the channel and/or a diffusion layer, and a cover sealing the groove.