ScotchTapeLord wrote ...

And what about the ISFET?

My chemistry major roommate mentioned that. It is certainly a transistor!

wrote ...
Well, this means that instead of applying current you apply voltage. A MOSFET is a very ON or OFF device. Mosfet's are not meant to be used linearly, as they produce excessive amounts of heat when compared to a transistor.

Mattski wrote ...

They're certainly not as common as the plain silicon BJT's and MOSFET's but digikey does carry many MESFETs and HEMT's for radio circuits. Anyway I didn't mean to get too far off track with those, I was just pointing out that "transistor" can refer to a wide variety of devices.

A couple more suggestions:

When talking about Darlington stages perhaps mention that one important application is in driving high power BJT's since those often have a current gain of only perhaps 20 while small signal BJT's have current gain more like 100, so the Darlington stage makes it easier to drive a high power BJT.

MOSFETs can be and are indeed used linearly, but it is more challenging to do this in discrete circuits largely because of threshold voltage variations between devices, whereas in a BJT the base emitter voltage drop is far more consistent, plus many (but not all) MOSFETs that are sold in discrete packages are intended for power applications and have been optimized for that. Also the heat produced by a transistor used in a linear fashion is not going to be very different whether it is a BJT or MOSFET.

Also a good thing to point out in the MOSFET section is that n-channel devices are usually superior to p-channel devices becaus of inherent physical properties, so for the same current rating a p-channel device will cost more and be slower. Maybe also point out that the higher current MOSFETs generally have higher input capacitance since both current and capacitance are proportional mainly to the size of the FET.