Abstract: The present method provides for the use as criterion the coefficient m of a deviation of the actual current-voltage characteristic of the p-n junction of a semiconductor device or integrated circuit under test obtained by applying a varying current in the forward direction through a p-n junction. The form of a current variation is chosen such that if the p-n junction has an ideal current-voltage characteristic ##EQU1## the current variation causes constant voltage increments through the p-n junction over the entire range of current values I. It means that for a p-n junction with an actual current-voltage characteristic ##EQU2## the increments obtained will be constant and proportional to the coefficient m. The apparatus for effecting the present method comprises at least two current generators controlled by a current controller, ensuring interrelated currents at their outputs. The current controller ensures that relative variations of each of the currents are equal.