Method of fabricating a switching regulator with a high-side p-type device

A first impurity region of a first type is implanted to have a first surface area on a substrate. A second impurity region of an opposite second type is implanted into a drain region of the transistor to have a second surface area in the first surface area of the first impurity region. A gate oxide is formed after implantation of the second impurity region between a source region and the drain region of the transistor, and the gate oxide is covered with a conductive material. A third impurity region of the opposite second type and a fourth impurity region of the first type are implanted into the source region of the transistor in the first surface area. A fifth impurity region of the opposite second type is implanted into the drain region of the transistor in the second surface area of the second impurity region.