Positron trapping in silicon deformed under high-stress conditions at room temperature is compared to that in Si plastically deformed at higher temperatures. After room temperature deformation, thermally rather stable vacancy clusters appear. o evidence for positron capture in dislocations is found. In contrast, after high-temperature deformatoin, positrons are trapped in rather large vacanvy clusters and in dislocations acting as combined positron traps. The specific features of positron trapping in silicon plastically deformed at room temperature are related to the dislocation core structure and to the inhomogeneous distribution of defects. ? 2004 WILEY-VCH Verlag Weinheim