An image-sensing device includes a semiconductor substrate including an image-sensing region and a peripheral circuit region surrounding the image-sensing region. The image-sensing device further includes an image-sensing element disposed in the semiconductor substrate in the image-sensing region, and an imaging processing element disposed in the semiconductor substrate in the peripheral circuit region. The image-sensing device further includes a first isolation element disposed in the semiconductor substrate in the peripheral circuit region and adjacent to the image-sensing element in the image-sensing region. The first isolation element includes a metal portion having a coefficient of heat conduction greater than 149 W/m·K, and an imaginary part of a permittivity (Im(ε)) of the metal portion under a light wavelength of 1100 nm is greater than 0.004.