This study was motivated by the possibility of using N resonant levels interacting with the GaAs conduction band, in GaNxAs1−x (0<x<2.5%), to enhance the density of states effective mass (md) and consequently the thermoelectric power factor (S2σ)—where S is the Seebeck coefficient and σ is the electrical conductivity. However, it was observed that, compared with GaAs, the power factor was reduced in spite of a small increase in the md. The influences of carrier passivation and dopant type, as well as the changes in the carrier scattering mechanism, which degrades the carrier mobility, are discussed.