A semiconductor transistor device includes a drift region, an insulating structure, a gate insulator, a gate electrode, a source, and a drain. The drift region includes a first lateral portion having a first dopant concentration and a second lateral portion having a second dopant concentration that is higher than the first lateral portion. The insulating structure is formed on the drift region and is disposed over a border between the first and second lateral portions such that hole generation is minimized in the drift region during operation.