Diode leakage current consists of diffusion (Id) and generation current (Ig), which is strongly sensitive to the residual defect density. These defects can be studied by activation energy (Ea). Therefore, this paper presents a method for calculating activation energy of silicon p-n junctions from volume generation current. It combines temperature-dependent current–voltage (I –V) and capacitance–voltage (C-V) measurements of diodes. The Ig can be found from the volume leakage current by subtraction of the volume diffusion current, which is calculated while the depletion width is zero. The activation energy (Ea) is derived from slope of an Arrhenius plot of Ig. To derive the correct slope the temperature dependence of the depletion width, which is obtained from the corrected volume capacitance has been applied. The Ea profile below junction has been shown. The lower Ea value has been found near the junction, which may relate to the junction implantation.