A high-strength zirconia-alumina composite ceramic substrate suitable for semiconductor devices has been invented. It is manufactured by a procedure starting with mixing powder formula of alumina, zirconia, and a self-made synthetic additive for ball milling in an organic solvent at room temperature. The resulting mixture is homogenously dispersed and is then subjected to the steps of slurry preparation, degassing, green embryo forming, punching, calculation, and sintering to yield the final composite ceramic substrate with an excellent mechanical property of three-point bending strength>600 MPa and superior thermoelectric properties of thermal conductivity>26 W/mK, insulation resistance>1014 Ω·cm and surface leakage current (150° C.)