Good point. Leakage current is the main issue these days, but that problem is only indirectly linked to power density. I've explained it your way in the past,

Good point. Leakage current is the main issue these days, but that problem is only indirectly linked to power density. I've explained it your way in the past, but I saw the Wikipedia article for Dennard scaling [1] says that power density for a transistor remains constant with time, which is true given that the underlying transistor technology has constant resistive losses. My understanding is that transistors using GaN have higher power density than "traditional" transistors, which mean Dennard scaling certainly breaks down. [1] https://en.wikipedia.org/wiki/Dennard_scaling https://en.wikipedia.org/wiki/Dennard_scaling