Surface chemical processes occurring on a Pd-nanoparticle-decorated tin oxide (SnO2) nanowire configured as a field-effect transistor (FET) can be strongly influenced by the gate potential if a high dielectric constant material is used as the gate oxide. Dramatic changes in channel currents are produced as a consequence when the device is exposed to hydrogen while operated in its depletion region, providing an example of gate-potential directed surface chemistry.