An image sensor device includes a semiconductor substrate, a radiation sensing member, a device layer, and a color filter layer. The semiconductor substrate has a photosensitive region and an isolation region surrounding the photosensitive region. The radiation sensing member is embedded in the photosensitive region of the semiconductor substrate. The radiation sensing member has a material different from a material of the semiconductor substrate, and an interface between the radiation sensing member and the isolation region of the semiconductor substrate includes a direct band gap material. The device layer is under the semiconductor substrate and the radiation sensing member. The color filter layer is over the radiation sensing member and the semiconductor substrate.