The invention belongs to the semi-conductor power device technical field. A SOI layer of the device is thinner (1to 2um); a grid oxide layer is thick (100 to 800nm); a grid field plate gets across a grid and extends above a drift region. An active expansion region positioned below the thick grid oxide layer and connected with a source region can be also arranged in the body of the device to assure the more effective formation of the whole device. The grid oxide layer of the invention is thicker, can bear high grid-source voltage and meet the need of a level displacement circuit; the SIO layer is thinner, can decrease the parasitic effect of the device and reduce consumption; through adding the grid field plate striding over the grid on the surface of the power device, the depletion of the drift region can be increased, the electric field peak value on the silicon surface at the tail end of the grid is decreased, the breakdown characteristic of the device is improved, further more the concentration of the drift region is helped to improve, and the on-state resistance of the device is decreased. The invention has the advantages of low parasitic effect, fast speed, low power consumption, strong radiation-resistant ability and so on, and is compatible with the standard process. By adopting the invention, various high-voltage, high-speed and low conducting loss devices of excellent performance can be produced.