In this work, we successfully develop of a high-power high-thermal conductivity GaN High Electron Mobility Transistors (GaN HEMTs). TSV (Through Silicon Via) structure can effectively improve heat dissipation and reduce the effect of thermal effects on devices. We compared the DC characteristics and the pulse measurement of current variation with time under different duty cycles between w/o TSV and TSV structure. We also introduce the Current collapse and self-heating effect in different pulse. Heat dissipation in high voltage and high frequency devices is a factor of major concern.