Inversion channel mobility of 4H-SiC(0001) metal-oxide-semiconductor field effect transistors (MOSFETs) has been investigated for its dependence on the re-oxidation annealing (ROA) conditions in a wet oxidizing ambient. The wet ambient was generated by a pyrogenic reaction of hydrogen and oxygen gas to control the water vapor content (rho(H2O)) in the ROA (pyrogenic ROA). It was found that rho(H2O) had a significant influence on channel mobility and it was increased significantly with higher rho(H2O) of about 25%, although the temperature and the time period were another important parameter. As a result, field-effect channel mobility for 4H-SiC MOSFETs increased to 47cm(2)/Vs by the pyrogenic ROA treatment with a rho(H2O) of 50%.