A method using a divided exposure technology is provided for restraining deterioration in the performance of a solid-state image sensor. A photoresist is formed over a semiconductor substrate and subjected to divided exposure. A dividing line for divided exposure is located at least over a region of a semiconductor substrate in which an active region in which a pixel is to be formed is defined. The photoresist is then developed and patterned. By utilizing the patterned photoresist, an element isolation structure for defining the active region in the semiconductor substrate is formed in the semiconductor substrate.