The main aim of this paper is to present the new design of an integrated planar spiral inductor with a new structure of an underpass to obtain a high inductance, high quality factor and minimum losses into winding and magnetic core. The performance of this structure dependent on the geometrical, electrical parameters and material properties. These parameters are calculated at 350 MHz and this is the high frequency used for MEMS applications. Furthermore, thermal analysis in inductor from finite difference method is described. The heat transfer model is based on heat conduction and heat convection. Moreover, the heat source is calculated by different losses. In addition, the simulation results from 3D finite element method using software also been presented in this paper. It is based on both the classical heat equation and certain condition limits. However, a new design of an underpass has been proposed where a via is fabricated with a circular layer. The input and output of the spiral are implanted in the same direction. In addition, the magnetic core is the solution to decrease the temperature. Finally, the results of the finite difference method are compared with simulation results from finite element method. The good agreement between the results is obtained. The proposed via and a core magnetic are responsible for enhancement the thermal behavior in integrated inductor. The result shows that the temperature of the air core inductor and magnetic core inductor could be 53 °C and 33 °C, respectively.