GaN material is one of the greatest advantages in Semiconductor Field with high frequency, high Temperature, high voltage, high saturation Velocity, high thermal stability, high switching speed and power electron device. The main advantage of the Isolation-Nitrogen ion implantation is it can pass device planarity and it will improve the fabrication yield. SiC is good for MISFET and GaN is good for HEMT device structure. There are some studies for AlGaN/GaN HEMT device structures with SiN passivation will impact on high breakdown voltage. GaN on Si as a substrate is a wide band gap device and large area to expensive bulk substrates. The deep states controlling the resistivity of these implant-isolated materials activation energy is in the range of 0.8-0.9eV. By using the ion implantation for particular area doping or isolation is a critical requirement for advancement of GaN device technology. GaN/AlGaN/GaN isolation device structure with ~5um epitaxial layer on the Silicon 111 substrate 100um width is done by the Nitrogen ion implantation with 30KeV, 120KeV and 140KeV with the dose of ~1e14cm-2 which covers the penetration depth around 0.45um in the active device region. Which showed a breakdown voltage of ~800V with Isolation gap between to metals is 4um and the Spacing between contact to contact is 10um. The impact of Isolation gap and Spacing are investigate with the breakdown voltage, Impact Ionization and the electric filed distribution.By Using Nitrogen Ion Implantation, the planar Isolation device is less cost and easy to manufacture. When the red sport is located at the edge of the contact edge device will have permanent damage which reduces the device performance and high gate leakage. These results are based on TCAD simulation by using Sentaurus Process and Sentaurus device which will have 90% of accurate results as experimental data