1. A solid-state image sensor comprising: a semiconductor substrate; photoelectric conversion units formed in said semiconductor substrate; microlenses formed above said semiconductor substrate so as to be positioned above the respective photoelectric conversion units; and a color filter which includes filter films arranged in a two-dimensional array and which is formed above said semiconductor substrate so that the filter films are positioned above the respective photoelectric conversion units, wherein each microlens is made of a low refractive index material and a high refractive index material, said photoelectric conversion units are a first photoelectric conversion unit and a second photoelectric conversion unit, said second photoelectric conversion unit being positioned below one of the filter films transmitting light of a longer wavelength than a wavelength of the light transmitted by another one of the filter films positioned above said first photoelectric conversion unit, and a volume of a high refractive index material included in one of the microlenses positioned above said second photoelectric conversion unit is greater than a volume of a high refractive index material included in another one of the microlenses positioned above said first photoelectric conversion unit.