A complementary metal-oxide semiconductor (CMOS)-based multichip flexible neural stimulator for retinal prostheses was developed. The multichip retinal stimulator is capable of simultaneous multisite stimulation. An on-chip stimulation generator was implemented on the "unit chip," which is the core device of the multichip retinal stimulator. The performance of the CMOS circuitry was characterized. A new device structure and packaging process was developed. The in vivo retinal stimulation on a rabbit's retina was successfully performed and the multisite stimulation functionality was confirmed.