This article presents a method to distinguish between the various conduction mechanisms through insulators in MOS structures whose expressions are exponential functions of voltage. This method accounts for the voltage drop (ΔV) across the parasitic resistance that could be significantly present in series with the MOS structure. This graphical method is based on a new Normalized Direct Conductance function to extract the value ΔV. The validity of the proposed method has been ascertained by using Silvaco TCAD simulations and measurements of the gate leakage current of an experimental n-channel MOSFET. The band diagram with the corresponding numerical values also verifies the extracted value of ΔV. It is concluded that the dominant conduction mechanism is Poole-Frenkel for the middle gate voltage region while Hot Electron Injection dominates for low- and high-voltage regions.