The present disclosure relates to oxide semiconductor transistors, methods of manufacturing the same, and/or memory devices including the oxide semiconductor transistors. The oxide semiconductor transistor includes first and second compound layers provided on a substrate, a channel layer in contact with the first and second compound layers, a first electrode facing a portion of the channel layer, a second electrode facing the first compound layer with the channel layer therebetween, and a third electrode facing the second compound layer with the channel layer therebetween. An oxygen concentration of a region of the channel layer facing the first electrode is greater than that of the remaining regions of the channel layer. A buffer layer may further be provided between the channel layer and the second and third electrodes. The first and second compound layers may include oxygen and a metal.