The invention provides a solid state imaging device with high photosensitivity. A lens resin coated on the surface of the device is subjected to an exposing treatment using lens masks and a developing treatment, thereby forming lens patterns. After improving the light transmittance of the lens patterns through irradiation of UV, the lens patterns are heated so as to form micro lenses each in the shape of a hemisphere. At this point, the heating temperature is set at a temperature lower than a temperature at which the lens patterns are completely melted. As a result, the lens patterns are prevented from flowing out, and a distance between the adjacent micro lenses becomes equal to a distance between the adjacent lens patterns. Accordingly, by making small the distance between the adjacent lens patterns, the light receiving area of each micro lens can be enlarged.