This paper reports on the effect of oxidation temperature on the thermoelectric performance of a plate-type thermoelectric power generator. Recently, thermoelectric power generation methods have attracted considerable attention as energy harvesting technologies. Among these, a plate-type thermoelectric power generator in which an Al layer is deposited on a Fe plate has been reported. Although oxidation of the surface of the Fe plate was verified experimentally to be effective in enhancing the thermoelectric performance, the kind of oxide suitable for a plate-type generator has yet to be investigated. In this study we oxidized the surface of an Fe plate at different temperatures, and plate-type thermoelectric power generators having various oxides at the bi-metallic interface were fabricated. It was found that Fe2O3 made a large contribution to increasing the Seebeck coefficient compared with Fe3O4. The generator with a bi-metallic interface oxidized at 400 °C showed the maximum power, the value being 1.4 μW at a temperature difference of 40 °C. Furthermore, we developed a theoretical model to predict the maximum power of a plate-type generator based on solid-state physics, and the predicted values were in good agreement with the experimental ones.