This work presents the modelling of impulsional pH variations in microvolume related to water-based electrolysis and hydrogen peroxide electrochemical oxidation using an ElecFET (Electrochemical Field Effect Transistor) microdevice. This ElecFET device consists of a pH-ChemFET (pH-Chemical FET) with an integrated microelectrode around the dielectric gate area in order to trigger electrochemical reactions. Combining oxidation/reduction reactions on the microelectrode, water self-ionization and diffusion properties of associated chemical species, the model shows that the sensor response depends on the main influential parameters as: (i) polarization parameters on the microelectrode, i.e. voltage (V p) and time (t p), (ii) distance between the gate sensitive area and the microelectrode (d), and (iii) hydrogen peroxide concentration ([H 2 O 2 ]). The model developed can predict the ElecFET response behaviour and creates new opportunities for H 2 O 2 –based enzymatic detection of biomolecules.