Abstract The phase transitions and habit changes of SiC crystals of the polytypes 2H, 3C, 4H and 15R have been studied in the conditions of a semiclosed SiC/C system, by annealing in argon at 1 atm pressure. In the temperature range of investigation (1500–2830 °C) all types transform to tabular crystals of the 6H structure. The transition of 2H whiskers into 6H crystals takes place via the metastable 3C modification. The experimental data are discussed in terms of models assuming either in situ volume transitions or surface mechanisms. The observed transition rates of normal crystals of 3C, 4H and 15R to 6H are considerably lower than the rate of the 2H→3C transformation of whiskers. From Arrhenius plots of the transition rates activation energies were derived which, within the limits of experimental accuracy, are equal (≈ 140 kcal/mole), and identicall with the activation energies of evaporation and of crystal growth by recrystallization of 6H. It is concluded that both for the transformations, where near-surface transport takes place, and for evaporation one and the same molecular step is rate controlling.