Transient recombination lifetimes have been measured in high‐purity,n‐type, float‐zone silicon from 4.2°K to room temperature. Photoconductivity decay curves and quiescent electrical conductivity values have been obtained by a microwave reflection technique which does not require electrical contacts to the sample. Experiments were performed at low injection levels on unirradiated samples and after irradiation with 30‐MeV electrons. An unusual feature of the data is a pronounced increase in lifetime with decreasing temperature below 45°K, similar to a trapping effect. This variation of lifetime with temperature has been explained using the two‐lifetime transient analyses of Sandiford and Wertheim. The temperature dependences of the capture cross sections are calculated and compared with the theoretical predictions of Lax and with other experimental results.