A method for manufacturing a SiC semiconductor device includes: forming an impurity layer in a SiC layer; and forming an oxide film on the SiC layer. The forming the impurity layer includes: implanting an impurity in the SiC layer; applying a cap layer on the SiC layer; annealing the cap layer to be transformed a carbon layer; annealing the SiC layer to activate the impurity; and removing the carbon layer. The annealing the SiC layer includes: increasing a temperature of the SiC layer from a second temperature to a first temperature within a first time duration; and decreasing the temperature of the SiC layer from the first temperature to the second temperature within a second time duration. The first temperature is equal to or higher than 1800° C., and the second temperature is lower than 1800° C. The first and second time durations are small.