Dislocation structure and planar faults have been examined in MoSi2single crystals deformed at high temperatures. Pure stacking faults were found in a crystal deformed at 900°C. The formation of the stacking fault is closely related to the phase stability of the C11band C40 ordered structures. Profuse stacking faults with increasing deformation temperature assist the ductility improvement of the MoSi2above about 1200°C. The critical resolved shear stress for {110}(331) and {013}(331) slip is determined in the temperature range 1000 to 1500°C.