An image sensor device includes a semiconductor substrate, a radiation sensing member, a device layer and a trench isolation. The semiconductor substrate has a front side surface and a back side surface opposite to the front side surface. The radiation sensing member is disposed in a photosensitive region of the semiconductor substrate and extends from the front side surface of the semiconductor substrate. The radiation sensing member includes a semiconductor material with an optical band gap energy smaller than 1.77 eV. The device layer is over the front side surface of the semiconductor substrate and the radiation sensing member. The trench isolation is disposed in an isolation region of the semiconductor substrate and extends from the back side surface of the semiconductor substrate.