This paper introduces the application of a reduced-order modeling technique for accurate temperature monitoring in Power Electronics modules. The methodology involves coupling the Finite Element Method with the radiosity equation to obtain high-fidelity models. These models account also for surface-to-surface radiation, an aspect that can have a high impact when the operating temperatures increase, and the components are close to each other. The Discrete Empirical Interpolation Method is employed to reduce the computation time with a limited effect on the accuracy of the prediction. Numerical and experimental results demonstrate the approach's effectiveness, showcasing high accuracy with minimal computation time and memory cost.