Each chemical reaction has its own energy profile that represents the energy changes during the transformation of reactants into products. Together with other sources, it provides information about the reaction mechanism. Here, we show how a complementary metal-oxide-semiconductor (CMOS)–compatible field effect transistor can be used to register an energy pathway of a chemical reaction. As a proof of concept we record an energy profiles (energy changes vs. reaction coordinate) of 3,3′,5,5′-tetramethylbenzidine oxidation catalyzed by horseradish peroxidase. This approach can be potentially extended to study other enzymatic and non-enzymatic reactions.