Semiconductor memory device

A semiconductor memory device includes: a substrate with first and second memory-cell array regions disposed on first and second substrate sides and first and second sense-circuit regions disposed on the first and second substrate sides between the first and second memory-cell array regions; first and second bitlines coupled to a plurality of memory cells in the first memory-cell array region; first and second complementary bitlines coupled to a plurality of memory cells in the second memory-cell array region; first and second column-selection transistors formed in the first sense-circuit region, and selectively couple the first bitline and the first complementary bitline to a first input/output (I/O) line and a first complementary I/O line; and third and fourth column-selection transistors formed in the second sense-circuit region, and selectively couple the second bitline and the second complementary bitline to a second I/O line and a second complementary I/O line.