A semiconductor device adapted for being disposed on a substrate is provided. The semiconductor device includes a pixel electrode, a drain, a semiconductor channel layer, a source, a gate insulation layer and a side-gate. The pixel electrode is disposed on the substrate. The drain is disposed on the pixel electrode and exposes a portion of pixel electrode. The semiconductor channel layer is disposed on the drain. The source is disposed on the semiconductor channel layer. The gate insulation layer is disposed on the substrate, at least covers the source and surrounds the semiconductor channel layer. The side-gate is disposed on the gate insulation layer and extendedly covers the substrate along at least one side of the gate insulation layer. An extending direction of a portion of the side-gate is identical to a stacking direction of the drain, the semiconductor channel layer and the source.