An electronic device and a manufacturing method thereof are provided. The electronic device includes a substrate, a buffer layer, an oxide semiconductor layer, and a gate electrode. The buffer layer is disposed on the substrate. The oxide semiconductor layer is disposed on the buffer layer and has a first part and a second part adjacent to the first part. The gate electrode is overlapped with the first part. A part of the buffer layer is overlapped with the second part of the oxide semiconductor layer, The part of the buffer layer has a first portion and a second portion disposed on the first portion. The concentration of boron in the first portion is greater than the concentration of boron in the second portion.