Disclosed are an oxide thin film transistor (TFT), a method of manufacturing the same, and a display panel and a display device using the same, in which a first conductor and a second conductor are provided at end portions of a semiconductor layer formed of oxide semiconductor. The first conductor and second conductor are electrically connected to a first electrode and a second electrode, and covered by a gate insulation layer. The oxide TFT includes a semiconductor layer provided on a buffer and including an oxide semiconductor, a gate insulation layer covering the semiconductor layer and the buffer, a gate electrode provided on the gate insulation layer to overlap a portion of the semiconductor layer, and a passivation layer covering the gate and the gate insulation layer.