Abstract: A microelectrochemical sensor having a diaphragm, a web, a first and a second electrode. The diaphragm is permeable to ions of a chemical species, is arranged transversely with respect to a cutout in a base body, and closes off the cutout in a fluid-tight fashion. The web is arranged on a first side of the diaphragm between a first partial surface and a second partial surface, and is designed to adjust a temperature of the diaphragm to an operating temperature using electrical energy. The first electrode has a first partial electrode and a second partial electrode, is permeable to fluid, and is arranged on the first side of the diaphragm. The web prevents electrical contact between the first electrode and the diaphragm. The second electrode has a third partial electrode and a fourth partial electrode, is also permeable to fluid, and is arranged on a second side of the diaphragm.