¡@In this study, the plastic deformation of (001) single crystal silicon at 900 oC is investigated by uniaxial compression along [001]. Using optical microscopy and scanning electron microscopy to observe the sample surface, and analysis the corresponding microstructure of different strain deformed silicon by transmission electron microscopy, particularly dislocation, slip systems and work hardening behaviour. ¡@Experimental temperature condition was chosen which over the BDT temperature range of silicon. We were found similar stages of work hardening described in metals and use the result of analysis dislocations and slip systems to suggest a hardening process of plastic deformation. ¡@The observations are similar to the feature in stage II (dislocation tangled) and stage III (dislocation cell structure). Partial dislocation and dipole are formed in less strained sample. We suggest a hardening process of plastic deformation from these results.