In this paper, a new GaN-based integrated module is designed to solve the problems encountered in the application of GaN devices, such as large parasitic inductance and thermal management problems. The layout of the integrated module is optimized to reduce the parasitic inductance. At the same time, different kinds of substrates are compared and the size of integrated module is studied. Finally, simulation and experiment results show that the layout has a small parasitic inductance of about 0.22 nH as well as a good heat transfer performance. Thermal simulation results are very close to experimental results. Besides, simulation results show that heat radiation must be considered in the thermal model because it accounts for a large proportion under natural convection.