A one-dimensional trapezoidal barrier potential U-0(x) with and without the image potential U;(x) was used to model three tunnel junctions: Al-Al2O3-Au (-Ag, -Cu) and calculate the junction I-V curves. As the effective trapezoidal barrier parameters are determined by fitting the calculated I-V curves to the experimental ones, it is found that if the I-V curves are calculated based on the barrier potential U-0 (x) + U-i(x), the parameters of the actual barrier U-0(x)-U-i(x) are obtained. Thus, the parameters of the actual trapezoidal barrier U-0(x)+U-i(x) can be obtained by extrapolating. The results show that the area of the actual U-0(x)+U-i(x) is smaller than that of the U-0(x) and for the Au-, Ag- and Cu-junction the area reduction is - 6.9, -5.4 and -4.2%, respectively. The variation of the barrier area reduction with the electrodes can be ascribed to the diffusion and oxidation reaction in the region of the junction interfaces, which results in smeared and indistinct interfaces and an increase in the actual distance between the metal mirrors of the two electrodes. (C) 2003 Elsevier Science B.V. All rights reserved.