The Dennard scaling law (also MOSFET scaling) is a scaling law that says roughly: as MOSFETs get smaller, their power density stays constant, so that the power use stays in proportion with area. Then, the voltage and current scale downward with length.
This has very real implications with chip fabrication. This effect allowed us to scale down from larger primitive transistors to packages suitable for VLSI, and increase transistor density. But we’ve gone so small that Dennard scaling doesn’t apply anymore and we can’t scale down further.