Thick film and direct bond copper (DBC) were successfully formed on aluminum nitride (AIN) ceramics. Commercially available gold (Au), silver-palladium (Ag-Pd), and copper (Cu) thick film pastes for alumina (AI2O3) were formed on AIN under exactly the same firing conditions as on AI2O3. From X-ray micro analysis (XMA) and X-ray diffraction (XRD) analysis, copper (Cu), lead (Pb), silicon (Si), and oxygen (O) were observed at the adhesive boundary of the thick films and ceramics. On the contrary, poor bondings were observed when bismuth (Bi) segregated at the adhesive boundaries. Pre-oxidation of AIN ceramics at high temperature around 1250°C was required for the bonding of DBC to AIN. Cu2O was formed at the boundary between the Cu metal and oxidized AIN, thus copper was directly bonded to AIN firmly. Bonding strength, peel strength, and wire bondability were enough for practical use in applications to high power modules and large-scale integrated (LSI) packages.