Methods of forming an oxide layer on silicon carbide include thermally growing an oxide layer on a layer of silicon carbide, and annealing the oxide layer in an environment containing NO at a temperature greater than 1175.degree. C. The oxide layer may be annealed in NO in a silicon carbide tube that may be coated with silicon carbide. To form the oxide layer, a preliminary oxide layer may be thermally grown on a silicon carbide layer in dry O.sub.2, and the preliminary oxide layer may be re-oxidized in wet O.sub.2.