A semiconductor device includes: a substrate; a seed layer disposed on the substrate; a compound semiconductor stack layer disposed on the seed layer; and a source metal layer and a drain metal layer disposed on the compound semiconductor stack layer. The semiconductor device further includes a conductive layer at least partially covering the source metal layer and the drain metal layer, and covering opposing side surfaces of the seed layer and opposing side surfaces of the compound semiconductor stack layer. The conductive layer electrically connects the seed layer and the source metal layer.