A multiplication phenomenon caused by fission fragments has been observed in 300 &OHgr;‐cm gold surface barrier detectors when operated at bias voltages greater than 100 V. This phenomenon occurs only for fission fragments that penetrate beyond some threshold depth for multiplication, and the threshold depth is found to decrease with increasing bias voltage. However, the effect could also be due to the surface properties of the detector making the depth correlation fortuitous. An analysis in terms of a threshold depth indicates that the multiplication may be due to a hole rather than an electron effect. No multiplication was observed for alpha particles with the same electric fields. P‐n diffused junction detectors operated at similar average electric field strengths did not show any multiplication effects.