In this second part, the mechanical behaviour of elemental semiconductors (ESC) and III-V compounds (CSC) is briefly reviewed. The marked temperature dependence of the stress-strain curve is recalled first and some attention is paid to the correlation between the lower yield stress and dislocation dynamics at moderate temperatures. In Si, some suitable pre-strain yields a very favourable situation where measurements of both mobile dislocation density and local stresses can be done and where activation parameters at the lower yield point fairly agree with those of dislocation glide. In CSC, polarity effects result from the very different mobility of α and β dislocations and activation parameters apparently fail to reproduce those derived from velocity measurements. Generally, the mechanical behaviour is affected by doping in the sense expected from velocity measurements, but « metallurgical » effects appear at high concentrations if doping atoms are mobile at the deformation temperature. At lower temperatures, SC can be deformed under high stresses, if brittle fracture is prevented by a confining pressure. Experimental techniques are discussed and present results point to different rate controlling mechanisms in this range, where environment effects are in addition suspected. A last section deals with the influence of non-doping impurities, using the best known examples of oxygen in Si and indium in GaAs.