Physics of autonomous refresh of FBC is presented. Current input to the floating body by impact ionization and output by charge pumping can balance to make FBC refresh by itself without sense amplifier operation. Thanks to this feature, multiple cells on a BL can be refreshed simultaneously, leading to a drastic reduction of BL charging current compared to the conventional refresh. 600μA refresh current for 1G-bit memory is achieved in 32nm technology node with 4ms retention time. If gate direct tunneling current is used as output, FBC can realize static RAM without periodical refresh when retaining data.