The present invention relates to a method used for forming a transistor structure at a substrate (SOI) which comprises a support silicon layer (1), an embedding insulating layer (2) and an upper silicon layer (3). The upper silicon layer has the upper layer thickness and comprises high doping level. The transistor structure comprises a grid area (G1), a source cathode and a drain area (5). The method further comprises that the grid area (G1) is formed at the upper silicon layer (3); the grid area (G1) is separated from the upper silicon layer (3) by a dielectric layer (GD); an opening area isformed at the upper silicon layer (3) which is distinguished by distinguishing oxide and/or containing a layer area (4); a high doping or a high destroyed area (5) is formed by insuring ions; the opening area (O1) is exposed to an ion beam (IB), wherein, the layer area (4) and the grid area (G1) are distinguished to be used for infusing a mask. The ion beam (IB) comprises the combination of beam energy and dosage and allows a high doping level area (L1) which is embedded into the source cathode and the drain area (5) in an insulating layer (2) in the upper silicon layer (3) and a high doping level or a high destroyed area (L0) under the grid area (G1) in the upper silicon layer (3) to be formed.