What is junction temperature, and what is a junction?

Answer 1

Could be several things.

In a semioconductor, like a transistor, a junctionis where two dissimilar semiconductors physically contact, such as n and p materials in a diode. The junction temperature would bethe temperature at this interface and governs some of the current generation processes going on at the junction.

Answer 2

The answer depends on the context, but as with the previous answer I assume that this is referring to a semiconductor junction. The junction temperature is generally quoted on semi-conductor device data sheets as a maximum value. Above this temperature the device is no longer guaranteed to work, but this is not the ambient temperature around the device or even the surface temperature of the device package, it is the temperature at the junction between p and n type semiconductor materials within the device itself.
Normally the data sheet will provide information on the thermal characteristics of the package or some graphs so that the junction temperature can be related to ambient or surface temperatures. Note that this is normally dependent on the power dissipation of the device.

Answer 3

In electronics it refers to the hottest internal temperature of a semiconductor; either an integrated circuit, or an individual transistor.

The "junction" is the PN junction of the transistor; either the base-to-emitter junction or base-to-collector junction of a bipolar transistor, or the gate-to-source or gate-to-drain junction of a JFET.

For integrated circuits, since there are sometimes millions of junctions, the junction temperature usually refers to either the hottest junction in the whole integrated circuit, or the one closest to the middle of the chip (if all junctions are running roughly the same temperature).

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