Abstract: The principle of deep trench termination for improving the avalanche breakdown of thedevice is studied. The effects of trench's depth and width, the field plate, the dielectric used to fill trench onthe avalanche breakdown voltage are analyzed using MEDICI. The results indicate that deep trenchtermination with field plate increases avalanche breakdown voltage of that of the device to 90% of that ofthe parallel plane junction. Meanwhile, the structure helps increase the cut-off frequency, the dissipationpower and the device reliability by decreasing the actual junction area and the surface leaking current.