The disclosure relates to a semiconductor device structure and a forming method thereof. The method comprises the steps: generating a first dielectric layer on a substrate, performing P type impurityion implantation and N type impurity ion implantation on the first dielectric layer to form a P-layer and a JFET layer; taking the middle region of the JEFT layer as a JFET region of a semiconductor device structure, and performing ion implantation on two sides of the JEFT region to form a body region of the semiconductor device structure; and performing ion implantation on the part of the body region to form a source region of the semiconductor device structure. According to the embodiment of the invention, the JFET region is arranged at the semiconductor device structures, so that the characteristic conduction resistance of the semiconductor device is reduced and thus the conduction speed is increased and the switching power loss is reduced. Moreover, because the P-region is arranged atthe JFET region, the gate oxidation reliability of the device can be improved, the gate-drain capacitance of the device can be effectively reduced, and the switching power loss can be further reduced.