The influence of temperature on the dark forward current-voltage characteristics of a single crystalline silicon solar cell and a small silicon diode within the range from 295-373 K has been analysed. It was shown that the forward voltage of the solar cell degrades 2 mV and in the case of diode 1 mV per 1 K temperature increases at constant forward current of 100 mA. Thermal resistance and heat transfer from the solar cell by using a thick copper plate as a heat sink have also been discussed. For the series resistance determination the current-voltage I-U characteristics of single crystalline silicon solar cells in different temperatures were measured in the dark. It was proved that series resistance of the silicon solar cells and diodes is temperature dependent and increases with temperature increase 0.65% K-1. Therefore, protection of silicon solar cells as well as silicon diodes against overheating is essential during their exploitation. Copyright (c) 2005 John Wiley & Sons, Ltd.