This study aims to contribute to the development of theoretical and experimental tools for characterizing the transport properties of perovskite semiconductors. In the context of existing transport characterization methods for perovskites, there is a need for techniques that can accurately assess the critical transport parameters, such as diffusion lengths, given the specific challenges posed, such as their inherent instabilities. The novel methodology employed involves the development of a theoretical model to describe the running fringes-induced photo-electromotive force (RF photo-EMF) effect in bipolar photoconductors with a rather general type of photoconductivity relaxation behaviors for both carriers. This model is founded on the theory of photoinduced space charge grating formation in semiconductors. Subsequently, RF photo-EMF experiments were conducted on methylammonium lead iodide (CH3NH3PbI3 or MAPI) polycrystalline films of varying grain sizes. By utilizing the RF photo-EMF technique, we successfully elucidated crucial transport and recombination characteristics, notably the ambipolar diffusion length and relaxation times of the charge carriers. Significantly, the developed theoretical model exhibited a remarkable agreement with the experimental results, highlighting its ability in explaining and predicting the behavior of charge carriers in perovskite semiconductors. The results of this study make a substantial contribution to the field of perovskite semiconductors by offering a novel theoretical and experimental approach to characterization of perovskites’ transport properties.