A new MOS BBD which can operate at extremely low voltage has been realized. A novel pentode MOS structure, having three overlapping gates, has been developed by introducing double poly-Silicon process. Making potential gradient along the channel length and excluding the stray capacitance, high transconductance and low channel length modulation are simultaneously obtained, and as a result, the transfer inefficiency is decreased. Consequently, the transfer inefficiency of2\times10^{-5}has been obtained even at 1.5V supply and 40kHz clock.