Definition
Leakage current is the current that flows through a transistor when it is nominally 'off' and not actively switching. It produces static power, dissipated continuously just because the chip is powered, independent of how much work the logic is doing. As process geometries have shrunk, leakage has grown from a rounding error into a major component of total chip power.
Where it comes from
The dominant source in modern CMOS is subthreshold leakage, current that trickles between source and drain because thinner transistors have lower threshold voltages and cannot fully turn off. A second source is gate leakage, where charge tunnels through the ultra-thin gate oxide of advanced nodes. Both worsen with temperature and with smaller geometries: subthreshold leakage can climb to a meaningful fraction of total power once feature sizes drop into the deep-submicron range.
Why miners should care
Mining ASICs chase the smallest, most efficient process nodes available, which are exactly the nodes where leakage is hardest to contain. Leakage is also strongly temperature-dependent, so a hot, poorly cooled chip leaks more, wastes more power as heat, and gets hotter still, a feedback loop that hurts efficiency and longevity. This is part of why keeping junction temperatures down improves J/TH, not just reliability. Techniques like power gating and high-threshold transistors exist specifically to fight it.
Cutting power to an idle block to stop this static loss is power gating; for how voltage choices influence it see voltage domain.
In Simple Terms
Leakage current is the current that flows through a transistor when it is nominally ‘off’ and not actively switching. It produces static power, dissipated continuously…