Disclosed are a complementary metal oxide semiconductor (CMOS) image sensor and a method of forming the same. The CMOS image sensor comprises a semiconductor substrate having a photodiode region and a transistor region. An optical path is formed between a micro lens on the photodiode region and a photodiode formed on the semiconductor substrate. The optical path comprises an inner lens formed between an intermetal insulation layer on the photodiode region and a transparent optical region formed on the inner lens. The transparent optical region generally has a different refractive index from the inner lens.