The invention discloses a 
semiconductor device and a manufacturing method thereof, and belongs to the technical field of semiconductors. The 
semiconductor device comprises a plurality of cells which are the same in structure and are sequentially connected with one another, wherein each 
cell comprises an N-type doped substrate, an N-type lightly doped epitaxial layer, a diffused P-type well region, a first P-type heavily dope region, an N-type heavily dope region, an oxidation layer, a 
metal cathode, a second P-type heavily doped region and a 
metal anode; the N-type lightly doped epitaxial layer is located on the N-type doped substrate; the diffused P-type well region is located in the N-type lightly doped epitaxial layer; the first P-type heavily dope region and the N-type heavily dope region are located in the diffused P-type well region; the oxidation layer is located on the upper surfaces of the N-type lightly doped epitaxial layer and the diffused P-type well region; the 
metal cathode covers the overall cells; and the second P-type heavily doped region and the 
metal anode are located on the lower surface of the N-type doped substrate. According to the 
semiconductor device disclosed by the invention, a semiconductor material which is opposite to the substrate in the 
doping type is injected into the back surface of the substrate, so that, on one hand, holes are injected into the N-type substrate and the N-type lightly doped epitaxial layer through P-type heavily doped back injection, the 
semiconductor device has two carrier currents, namely a hole current and an 
electron current, and the 
current density of the device is increased; and on the other hand, the reverse withstand 
voltage of the device can be improved.