You do realize that "vacuum tubes" are also called "thermionic valves", right?

That is correct. When you excite the outer shell of electrons, causing them to jump to a higher energy state, and allow conduction, you have added energy (heat) to the system. However you want to go about supplying that heat to the system, you have heated it up, and heating it up has in turn make the semiconductor conductive. It is a thermally regulated electric device.

Yes. You apply an electric field to the semiconductor, energizing a percentage of the atoms beyond the band gap, opening up holes to allow conduction. You add energy to the system. In other words, you raise the temperature.

Yes. That is how a semiconductor functions. At low temperatures, you're below the band gap, requiring energy be supplied to excite the atoms, bump electrons to a higher shell, open holes, and increase conductivity. At high temperatures, you're above the band gap, and you can't function because you're always a conductor.

What controls the band gap? Supplying energy to excite atoms and cause electrons to jump to the next shell, opening up holes that increases electrical conduction. What defines the amount of energy in an atom? Heat. What is the measurement for bulk heat density? Temperature. So, as temperature goes down, the heat content goes down, and energy state goes down. The semiconductor becomes an insulator. As temperature goes up, heat content goes up, energy state goes up, and you're now a conductor. Hence, semiconductors are fundamentally thermally controlled electric (thermoelectric) devices.

If your chip's temperature brings the energy level above its band gap, your semiconductor will simply not function, and this temperature is well below your semiconductors functional mechanical limits. If your chip's temperature means the energy level is well below the band gap, your semiconductor will need to run at a high core voltage and consume a large amount of power to bring the energy level (and temperature) of the gates up such that they will conduct and switch.

The problem is that transistors are thermoelectric devices. You switch them on and off by heating them up to change their conductivity. Silicon chips can withstand temperatures well beyond the point at which the plastic packages they are mounted to break down, but that temperature is also well beyond their switching point, making them useless as a computational device.

If you could produce a semiconductor that was useful at 3000F, then that would be its normal operating temperature, and you would need to feed it a high enough core voltage to allow it to heat itself up to that temperature to switch.

The entire side of the card is one giant heatsink, shared between the two dies. The heatsink is separate from the dies by a heatspreader, basically a giant flat heatpipe, to ensure roughly equal cooling between the two dies.

Are you suggesting that heatsinks work by absorbing and storing the waste heat generated by the CPU?

Except we don't use copper any longer, we use ammonia and a passive refrigeration cycle.

In fact, heatpipes being a form of phase change cooling, are much more efficient than pumped water at short and medium ranges. The only issue with heatpipes is that the average hobbyiest can't make them themselves, and they require static routing.

There's no problem with convecting your heat near the thing you actually want to cool, so long as you can get enough airflow there.

Except in this case, it's carrying the heat to a single 120mm exhaust port, instead of the entire surface area of that huge card it would have otherwise normally had.

That really sounds like a flaw in your case than the radiators contained within it. Back when we had blow-down heatsinks instead of tower ones, cases would come with side vents and shrouds to provide cool air directly to the fans. If you open up a server case, chances are it will have a shroud that covers both CPUs and all your memory, ducting air directly from several of the mid-plane fans. You can get cases that move the power supply to the bottom, so the CPU is directly in the top rear corner of the case, next to exhaust fans. You can get cases that rotate the board sideways so that everything vents upwards, taking advantage of convection to prevent recirculation outside the case.

A standard GPU heatsink is really god damned big. It's about an inch thick, and extends the entire length of the card, with a big centrifugal blower fan at one end, and exhaust vents out the back of the case on the other. The 120mmx20mm radiator they replaced it with is actually smaller.

In this case, they're sacrificing the blower fan, rear exhaust, and all that surface area directly on the card, for a single 120mmx20mm radiator that gets mounted to the back of your case. Using water cooling to feed a giant external heat exchanger is beneficial compared to traditional air exchangers directly in the case. "closed loop" water cooling systems are nothing more than the Monster cables of the heat sink market.

Or a dremel. Just cut off the remaining pins for the extra channels and it works fine. You can even test it out by taping off those pins and mounting it in an x16 slot.