•A carbon–silica material derived from rice husk agricultural waste is prepared.•The improved thermal stability can be achieved by deduced the ionic content.•The thermal-mechanical strength and thermal conducting of epoxy/BRH are improved. The present study focused on the preparation and characterization of a bio-based carbon-silica material derived from rice husk agricultural waste and its function in epoxy matrix for electronic packaging applications. X-ray diffraction (XRD) analysis, N2 adsorption/desorption isotherms, and scanning electron microscopy were used to characterize the structure as well as morphology of the resultant carbon–silica material, namely black rice husk ash, called BRH. Thermogravimetric analysis results suggest that improved thermal stability can be achieved by reducing the ionic content of the BRH materials through the pre-acid-hydrothermal technique. The ionic content of Cl−, Na+, and K+ of the BRH sample respectively were 4.3, 9.8, and 9.0ppm after further post-hydrothermal process. In addition, the XRD diagram shows that the structure of the calcined BRH material, is in amorphous form, which is non-toxic to humans. For packaging application, an improvement of 147% in storage modulus and 49% in CTE by the addition of 46% filler was realized. In addition, compared with pure polymer, the thermal conductivity values of the epoxy/pre-BRH composites were improved by 142%. From these results, it was concluded that this BRH filler derived from waste rice husks can promote the thermal stability, thermal-mechanical strength, and thermal conduction of the Epoxy/BRH composites. Display omitted