Abstract: The present invention provides an image sensor and a method for fabricating the image sensor. The image sensor includes a semiconductor substrate, photodiodes (PD), deep isolation trenches, first deep P-well blocks and second deep P-wells. The isolation trenches surrounds the PDs, and each of the isolation trenches is separated from any adjacent isolation trenches at a crossing where they would have crossed each other if they further extended. The first deep P-wells blocks have projections on the semiconductor substrate, which encompass projections of said separated portions of the isolation trenches on the semiconductor substrate. The first P-well blocks can be formed using only one photomask, resulting in a reduction in cost.