Abstract: A semiconductor package which comprises a lead frame, a semiconductor chip secured to the lead frame and a mold composition encasing the lead frame and the semiconductor chip has a filler of ceramic particles. Each of the ceramic particles, preferably silica or alumina, has macroscopic pores of sufficient size to receive a resin binder therein, the pores extending from the surface of the particle to the particle interior. A permanently hardenable composition adherable to the ceramic particles preferably an epoxy cresol novolac, extends around the ceramic particles and into the pores. The ceramic particles are formed by providing ceramic particles having a macroscopically smooth surface and subjecting the surfaces of the particles to a composition capable of removing portions of the particles, preferably hydrofluoric acid, while agitating the particles to form the pores.