The response of a Pd–SiO2–Si hydrogen sensor depends on the reaction kinetics of hydrogen on the Pd surface and on the hydrogen adsorption states at the Pd/SiO2 interface. In this work we show that besides the dominating hydrogen adsorption state located on the oxide side of the interface, a second state, resulting in opposite hydrogen polarization, exists. This state is possibly a reminiscence of the hydrogen adsorption state on a clean Pd surface. Taking both states into account, a simulation of the hydrogen response over more than ten decades in hydrogen pressures gives good agreement with published data. © 1998 American Institute of Physics.