Bulk single crystals of 4H-SiC have been deformed in compression at low strain rates in the temperature range 900 degreesC-1360 degreesC and their microstructures have been observed by TEM. Results of mechanical tests show that the Variation of the yield stress as a function of temperature is not monotonous but decreases strongly for T>1100 degreesC. It is observed that deformation proceeds by leading Si(g) partials at T<1000C, total dislocations at T>1200 degreesC and mixture of leading Si(g) partials and total dislocations between 1050 degreesC and 1150 degreesC.