Transistor Tetrodes

We’ve all used n-p-n and p-n-p bipolar transistors with three connections but I had never heard of transistor tetrodes until I was researching this article. Transistor tetrodes have four leads and come in different variations. Remarkably they have two control elements instead of one, that’s two base (b) connections for bipolar transistors and two gate (G) connections for MOSFETs.