Temperature-and thickness-dependence studies on silicon-carbide composites (fired matrices of silicon-carbide crystallites, clay and graphite) have produced a new insight into the electrical-conduction mechanisms in such devices. Using computer methods, an optimum empirical expression for the current/voltage characteristic has been obtained in the formI=C1exp (αT)V/L2+C2exp (βT)V3/L5+C3exp (δT)V6/L7whereTis the device temperature andLis the device thickness. The most probable explanation for this equation is that it represents three different electric-field modes of space-charge-limited current flow. The silicon-carbide composite can be thought of as a bulk polycrystalline insulator or semiconductor in which the crystallite-crystallite contact points act as ‘grain boundaries’, the clay holds the crystallites together and the graphite is an impedance moderator; The linear conduction term can be explained by assuming that the carrier drift velocity is independent of electric field at low fields (<1.5 × 103V/m). TheV3/L5term is due to the field-dominated double-injection process, while the conduction region represented by theV6/L7term is most probably the diffusion-dominated double-injection process.