A method for manufacturing a vertical power semiconductor device is provided, wherein a first impurity is provided at the first main side (103) of a semiconductor wafer (101). A first oxide layer (112) is formed on the first main side (103) of the wafer (101), wherein the first oxide layer (112) is partially doped with a second impurity in such way that any first portion of the first oxide layer (112) which is doped with the second impurity is spaced away from the semiconductor wafer by a second portion of the first oxide layer (112) which is not doped with the second impurity and which is disposed between the first portion of the first oxide layer (112) and the first main side (103) of the semiconductor wafer (101). Thereafter a carrier wafer (115) is bonded to the first oxide layer (112). During front-end-of-line processing on the second main side (102) of the semiconductor wafer (101), the second impurity is diffused from the first oxide layer (112) into the semiconductor wafer (101) from its first main side (103) by heat generated during the front-end-of-line processing.