A semiconductor device includes a substrate, a semiconductor layer, light-sensing devices, a transparent dielectric layer and a grid shielding layer. The semiconductor layer overlies the substrate, and has a first surface and a second surface opposite to the first surface. The semiconductor layer includes microstructures disposed on the second surface of the semiconductor layer. The light-sensing devices are disposed on the first surface of the semiconductor layer. The transparent dielectric layer is disposed on the second surface of the semiconductor layer, and covers the microstructures. The grid shielding layer extends from the first surface of the semiconductor layer toward the second surface of the semiconductor layer, and surrounds each of the light-sensing devices to separate the light-sensing devices from each other, in which a depth of the grid shielding layer is greater than two-thirds of a thickness of the semiconductor layer.