An image sensor device includes a substrate, a pixel circuit, a dielectric structure, a photo sensitive element, a grid, and a convex dielectric lens. The substrate has a first side and a second side opposite to the first side. The pixel circuit is disposed on the first side of the substrate. The dielectric structure is disposed on the second side of the substrate. The photo sensitive element is disposed between the pixel circuit and the dielectric structure. The grid is disposed on the dielectric structure. The convex dielectric lens is disposed on the dielectric structure. The convex dielectric lens has a convex side. A topmost of the convex side is above an interface between the dielectric structure and the grid.