The present invention provides a semiconductor device including a semiconductor substrate having a first conductive type, at least one high-side transistor device and at least one low-side transistor device. The high-side transistor device includes a doped high-side base region having a second conductive type, a doped high-side source region having the first conductive type and a doped drain region having the first conductive type. The doped high-side base region is disposed within the semiconductor substrate, and the doped high-side source region and the doped drain region are disposed within the doped high-side base region. The doped high-side source region is electrically connected to the semiconductor substrate, and the semiconductor substrate is regarded as a drain of the low-side transistor device.