This paper compares the behavior of the gate oxide in 4H-SiC lateral MOSFETs subjected to post-deposition annealing (PDA) in N 2 O and POCl 3. A significantly higher channel mobility was measured in 4H-SiC MOSFETs subjected to PDA in POCl 3 (108 cm 2 V− 1 s− 1) with respect to N 2 O (19 cm 2 V− 1 s− 1), accompanying a reduction of the interface traps density. Hence, a different temperature coefficient of the mobility and of the threshold voltage was observed in the two cases. According to structural analysis, the gate oxide subjected to PDA in POCl 3 showed a different surface morphology than that treated in N 2 O, as a consequence of the strong incorporation of phosphorous inside the SiO 2 matrix during annealing. This latter explained the instability of the electrical behavior of MOS capacitors annealed in POCl 3.