A semiconductor device includes a first semiconductor layer, a first electrode above and electrically connected to the first semiconductor layer, a second electrode above the first semiconductor layer and electrically connected to the first semiconductor layer, a first insulating layer above the first semiconductor layer between the first and second electrodes, and a third electrode. The second electrode is spaced from the first electrode along the first semiconductor layer. The third electrode includes a first portion above the first insulating layer between the first and second electrodes, and a second portion between the first portion and the second electrode and extending from the first portion in the direction of, and spaced from, the second electrode. The distance between the first semiconductor layer and an adjacent curved surface of the second portion gradually increases from the first portion to the end of the second portion distal the first portion.