The ability of thermoelectric power measurements to permit a description of carrier‐density and phonon‐drag variations caused by photoexcitation was tested in 100‐&OHgr;·cmn‐ andp‐type silicon. At low temperatures the major effect of photexcitation is to decrease the phonon‐drag contribution to the thermoelectric power by increasing the phonon density in the crystal. At higher temperatures the thermoelectric effect can be used to investigate changes in the electronic contribution due to photoexcitation. An apparently anomalous increase in thermoelectric power with photoexcitation was consistently found inp‐type silicon over an intermediate temperature range.