A simple one-step procedure is introduced for the preparation of diazonium−enzyme adducts. The direct electricallyaddressable deposition of diazonium-modified enzymes is examined for electrochemical sensor applications. Thedeposition of diazonium−horseradish peroxidase leads to the direct electron transfer between the enzyme and electrodeexhibiting a heterogeneous rate constant, ks, of 10.3 ± 0.7 s-1 and a ΔEp of 8 mV (v = 150 mV/s). The large ks andlow ΔEp are attributed to the intimate contact between enzyme and electrode attached by one to three phenyl molecules.Such an electrode shows high nonmediated catalytic activity toward H2O2 reduction. Future generations of arrayedelectrochemical sensors and studies of direct electron transfer of enzymes can benefit from protein electrodes preparedby this method.