A semiconductor image sensor includes a substrate having a first side and a second side that is opposite the first side. An interconnect structure is disposed over the first side of the substrate. A plurality of radiation-sensing regions is located in the substrate. The radiation-sensing regions are configured to sense radiation that enters the substrate from the second side. The radiation-sensing regions are separated by a plurality of gaps. A plurality of radiation-blocking structures is disposed over the second side of the substrate. Each of the radiation-blocking structures is aligned with a respective one of the gaps. A plurality of color filters are disposed in between the radiation-blocking structures.