Passivation is generally used to suppress the current collapse, however, it also cause the decrease in breakdown voltage. By incorporating a field plate, the breakdown voltage was enhances from 46 to 148V as tested using the drain current inject technology (DCIT), which indicates that the field plate can increase the breakdown voltage remarkablely. Then, comparisons between the degrees of current collapse in the conventional HEMTs, the HEMTs after passivation and FP-HEMTs indicate that the field plate performs better in suppressing current collapse than passivation. It is conclusded that adopting the field plate structure is a good solution to the problem of incresing the breakdown voltage and at the same time suppressing the current collapse in GaN HEMTs.