In this work a modification of Terman method for determination of interfacial energy states located in the forbidden energy gap of the semiconductor (interface states) convenient for application in metal—high-κ—Si structures is proposed and explained in details. It has been found that usually observed presence of tails in the distribution of interface states towards the band edges is an artifact due to the method of determination of interface state densities. While excluding the contribution of quantum charge in semiconductor close to the interface with dielectric, these tails in the distribution disappear. Simple efficient method for determination of total density of interface states over the silicon bandgap is proposed.