Jonker plots (Seebeck coefficient versus logarithm of conductivity) have been utilized to obtain the product of the density of states (DOS) and mobility (μ) in oxide semiconductors, from which the maximum electrical conductivity can be estimated for degenerate transparent conducting oxide (TCO) applications. In addition, the DOS–μ product can be utilized to predict the maximum achievable “power factor” (PF, Seebeck coefficient squared times conductivity) for oxide semiconductors. The PF is an important parameter governing the figure of merit for thermoelectric oxide (TEO) applications. The procedure employs an analysis developed by Ioffe, and provides an important screening tool for oxide (and other) thermoelectric materials, based upon data from polycrystalline ceramic specimens. Several oxides, including known transparent conductors, are considered as TCO and TEO case studies in the present work.