Many of the properties of Si-based ceramics, including their structural behavior, are strongly influenced by their micro/nanostructure and by the microscopic residual stress fields piled up during processing and/or usage. The electron beam, used as a sharp and reliable probe for high-resolution cathodoluminescence (CL) assessments, can routinely provide a suitable tool for assessing both the structural and the mechanical characteristics of Si-based ceramics on a sub-micrometer scale. Although the full development of stress-related CL techniques is still in embryo, we show here the possibility of assessing microscopic stress fields inside a field-emission gun scanning electron microscope (FEG-SEM). This new assessment takes advantage of the piezo-spectroscopic effect on selected bands of CL spectra and it is applied here to both β-silicon nitride (Si3N4) and β-silicon carbide (SiC) ceramics. CL spectra in both materials arise from their peculiar optically active defects. Experimental assessments of microstress fields may open a completely new perspective in the development of high-performance Si-based ceramics because one can directly visualize how residual stresses distribute within the material micro/nanostructure and miniaturized devices.