A semiconductor device includes a semiconductor substrate, a field oxide layer, a gate region and field plate integrated structure and a plurality of contact holes. A body region and a drift region are formed in the semiconductor substrate. An active region is formed in the body region, and a drain region is formed in the drift region. A field oxide layer is located on the drift region and the drift region surrounds a part of the field oxide layer. An integrated structure including a gate region and a field plate, the integrated structure extending from above the field oxide layer to above the body region. A depth of a contact hole closer to the source region penetrating into the field oxide layer is greater than a depth of a contact hole closer to the drain region penetrating into the field oxide layer.