A simple electrostatic model of the adsorbate–adsorbate interaction of hydrogen atoms at aPd–SiO2interface is presented. The model predicts a hydrogen adsorption isotherm of the Temkin type. It is found that, in practice, an upper limit for the hydrogen response of a Pd-metal-oxide-semiconductor device exists. The value (in V) is equal to the difference of the initial heats of adsorption (in eV) of the interface and the Pd bulk, respectively. Furthermore, a corresponding maximum hydrogen concentration, at the interface, of1×1018 m−2is predicted. The predictions are in good agreement with previously observed experimental data. ©1997 American Institute of Physics.