Abstract: A semiconductor device includes a semiconductor stack, a third semiconductor structure, a dielectric layer, and a reflective layer under the third semiconductor structure. The semiconductor stack includes a first semiconductor structure, an active structure, a second semiconductor structure. The first semiconductor structure has a first surface which includes a first portion and a second portion, and the first surface has a first area. The third semiconductor structure connects to the first portion, and has a second surface with a second area. The dielectric layer connects to the second portion and includes a plurality of openings, and the plurality of openings have a third area. A ratio of the second area to the first area is between 0.1˜0.7, and a ratio of the third area to the first area is less than 0.2.