In situ straining experiments in a high-voltage electron microscope have been carried out for the first time on MoSi2 single crystals between 800 and 1000 degrees C along a soft [201] orientation. Dislocations with 1/2[111]Burgers vectors were formed in localised sources leading to almost planar slip. The dislocations were strictly arranged along 60 degrees and edge orientations and moved at high velocities or in a viscous way. These observations are correlated to the macroscopic deformation behaviour and interpreted by the formation of intrinsic point defect atmospheres around the moving dislocations. The model explains the 'inverse' dependence of the strain rate sensitivity of the flow stress on the strain rate.