Abstract The recombination of excess hot carriers in germanium has been investigated by measuring the change in photoconductivity caused by exciting samples with 2.85 kMc microwaves up to peak fields of 10 4V/cm. Microwave rather than d.c. pulse excitation was used, and other precautions taken, to avoid sweep-out of excess carriers. Samples whose lifetimes were determined by surface recombination and by recombination at copper impurities in the bulk were investigated in this manner. In all these samples a decreased photoconductivity was observed immediately following the microwave pulse, indicating enhanced recombination in the high field. Comparison of the experimental results with theory indicates that the cross section for electron capture of singly charged copper centers decreases with increasing speed of the carriers.