A power transistor device including a substrate structure, a first conductive layer, a second conductive layer, and a third conductive layer is provided. The substrate structure has a base portion and fin portions. The fin portions protrude from a surface of the base portion. The first conductive layer is disposed across the fin portions and has a first side and a second side opposite to each other. The second conductive layer is disposed across the fin portions and is located at the first side of the first conductive layer. The third conductive layer is disposed across the fin portions and is located at the second side of the first conductive layer. The first conductive layer, the second conductive layer, the third conductive layer, and the fin portions are insulated from each other. An extending direction of the first, second, and third conductive layers intersects a length direction of the fin portions.