We propose a flex-pass-gate SRAM (Flex-PG SRAM), which is a FinFET-based SRAM to enhance both the read and write margins independently. The flip-flop in the Flex-PG SRAM consists of usual FinFETs, while its pass gates consist of double-"independent"-gate FinFETs, i.e., "four-terminal"-(4T-) FinFETs. A 4T-FinFET has a variable threshold voltage controlled by the second gate voltage. This function enables the Flex-PG SRAM to optimize the current drivability in the pass gates according to operational conditions of read and write. This results in enhancement of both the read and write margins. TCAD simulations revealed that the Flex-PG SRAM increases the read margin by 71 mV without the cell size penalty and decrease in the write margin, even when its 6 sigma tolerance is ensured. Also, a half-cell experiment proved its feasibility. (C) 2008 Elsevier Ltd. All rights reserved.