In order to alleviate the leakage current of AlGaN/GaN High Electron Mobility Transistors (HEMT) device with the N-type GaN buffer, the new Al0.25Ga0.75N/GaN HEMT with the Fluoride ion implantation is proposed for the first time in this paper. Firstly, the output characteristic has the ohmic characteristic for the AlGaN/GaN HEMT without acceptor-type trap, which explains why Fe and Mg are doped into the GaN buffer layer as reported in the literature in theory and simulation. By using the output characteristics of the Ids-Vds for the AlGaN/GaN HEMTs with and without low density drain, the results are obtained that fluoride ion implantation can capture effectively the electrons emitted from the source to reduce the leakage current of the GaN buffer compared with fluoride ions in the gate and the drain regions. The breakdown voltage goes up to 262 V. The scientific basis is set up for desiging the new AlGaN/GaN HEMT with both the low leakage current and the high breakdown voltage.