A prototype of oxide thermoelectric module consisting of p-NaCo2O4/n-ZnO sintered materials was successfully fabricated for electrical power generation by applying a diffusion welding technique without filler metals. The power generation characteristics examined in the high temperature region revealed that the diffusion welding technique under a condition of 16 MPa at 1023 K in Ar was suitable to joint the sintered oxide materials with silver conducting strips. Twelve pairs of p- and n-oxides were connected in series with a planar arrangement in a square area of 30x30 mm(2). A maximum power output of 58 mW was obtained at a temperature condition of T-H/T-L = 839/377 K, and no deterioration in power output was observed even after twenty times of heat cycling.