We propose to acquire operando scanning X-ray diffraction microscopy (SXDM) maps on Al(Ga)N/GaN-based HEMT devices in operation mode. The study aims to probe the lattice distortion in the active layer of the device due to inhomogeneities in the electric field and temperature distribution. The results will help to bench-mark other techniques, such as micro-Raman scattering and device modelling.