The interfacial layer theory considering the effects of the interface states and surface fixed charges is developed for the barrier height of the Schottky barrier diode with a thin uniformly doped surface layer. It is shown that the origins of the barrier height modification using the highly doped surface layer are mainly due to the increase of the electric field at the contact surface and the change of the interface properties. Design criterion for the maximum width of the highly doped surface layer is derived and calculated in detail for nickel barrier metal onn‐type silicon with the specificed interfacial layer conditions. Comparisons between the the developed expression of the barrier height reduction with respect to the ion dose and the experimental data of Shannonetal. are made, which tend to support the proposed model.