The influence of a strong electromagnetic field on the currents and electromotive forces in the p–n-junction is considered.It is shown that under the influence of an electromagnetic wave the p–n-junction becomes a source of electromotive force (EMF) dependent on the current. Obtained, analytical expression for EMF and internal resistance of such source. From the experimental graphs of the current-voltage characteristic of the p–n-junction placed in a strong microwave (microwave) electromagnetic field, plot sof the dependence of the EMF and internal resistance on currents through a diode are obtained.