MoSi₂ single crystals in the soft <201> orientation and polycrystals were deformed in constant strain rate tests in compression between 300 and 1200^°C for single crystals, and between 495 and 1250^°C for polycrystals. Stress relaxation and temperature change tests were performed to determine the activation parameters of the deformation. In addition to conventional transmission electron microscopy in a high-voltage electron microscope, in situ straining experiments were carried out in this instrument to observe the deformation processes directly. A new model is proposed to interpret the flow stress anomaly in MoSi₂ single crystals. In polycrystals, the deformation is controlled by dislocation glide below about 1050^°C, however, by decohesion of a grain boundary phase above this temperature.