A biochemical sensor is provided for measuring the concentration of a chemical dissolved within a fluid by providing a differential voltage proportional to a temperature differential resulting from the heat evolved from the enzymatic reaction of the chemical under test. The biochemical sensor is formed by depositing thin films of two dissimilar metals upon a substrate using microelectronic fabrication techniques. A multiplicity of thermocouple junctions are created at the intersections of the two dissimilar metal films, and the resulting series-connected thermocouple junctions are alternately designated sensing and reference junctions. The sensing junctions, but not the reference junctions, are covered by an enzyme, catalyst, or other species for initiating a chemical reaction involving the chemical under test, giving rise to a temperature differential between the sensing and reference junctions proportional to the concentration of the chemical under test. The biochemical sensor may be implanted within a human body for continuously monitoring concentrations of glucose or other chemicals present within the bloodstream.