Experiments in which silicon p‐n junctions have been used as detectors of fission fragments and elastically scattered heavy ions are described. The curve of pulse height versus energy for carbon particles is linear and passes through the origin. Points for Cf252fission fragments and alpha particles fall on the curve determined by the carbon‐particle points. This result implies that the energy required for electron‐hole pair formation is the same for the three types of particles. Also, no ``ionization defect'' is observed for the fission fragments. Some other possible uses for the detectors of this type are suggested.