Semiconductor-based photodetectors (PDs) convert light signals into electrical signals via the photoelectric effect, which involves the generation, separation, and transportation of the photoinduced charge carriers, as well as the extraction of these charge carriers to external circuits. Because of their specific electronic and optoelectronic properties, metal oxide semiconductors are widely used building blocks in photoelectric devices. However, the compromise between enhancing the photoresponse and reducing the rise/decay times limits the practical applications of PDs based on metal oxide semiconductors. As the behaviors of the charge carriers play important roles in the photoelectric conversion process of these PDs, researchers have proposed several strategies, including modification of light absorption, design of novel PD heterostructures, construction of specific geometries, and adoption of specific electrode configurations to modulate the charge-carrier behaviors and improve the photoelectric performance of related PDs. This review aims to introduce and summarize the latest researches on enhancing the photoelectric performance of PDs based on metal oxide semiconductors via charge-carrier engineering, and proposes possible opportunities and directions for the future developments of these PDs in the last section.