A cost-efficient self-terminated write driver is proposed for low-energy RAM and logic circuits by using spin-transfer-torque (STT)-magnetic tunnel junction (MTJ) devices. Since a bidirectional write current is required for STT switching, data-dependent write-completion monitoring, where the node with large voltage difference between before and after the switching is selectively used, makes it possible to achieve sufficiently large sense margin at any write current directions. By the enhancement of sense margin, write-completion monitoring and self-write-termination circuitries are simplified. Thus, 60% of transistor counts reduction and further robust write-completion detection under process variation are achieved in comparison with those of the prior work.