A method of manufacturing a silicon carbide semiconductor device is provided that includes a step of forming in a surface of a silicon carbide wafer of first conductivity type a first region of second conductivity type having a predetermined space thereinside by ion-implanting aluminum as a first impurity and boron as a second impurity; a step of forming a JTE region in the surface of the silicon carbide wafer from the first region by diffusing the boron ion-implanted in the first region toward its neighboring zones by an activation annealing treatment; a step of forming a first electrode on the surface of the silicon carbide wafer at the space inside the first region and at an inner part of the first region; and a step of forming a second electrode on the opposite surface of the silicon carbide wafer. Thereby, a JTE region can be formed that has a wide range of impurity concentration and a desired breakdown voltage without increasing the number of steps of the manufacturing process.