A bipolar transistor has two semiconductor junctions in a three layer sandwich...................
In fact that was just a question to me. I'm trying to know what's going on in a transistor.
.......................
This is N-doped (collector), P-doped (base), N-doped (emitter) semiconductor material for an NPN transistor.
Reverse that for a PNP.
If you measure each of these junctions with an ohmmeter, they will look like a normal junction diode with the base being the anode and the collector and emitter the cathodes (for an NPN).
During normal operation the base-emitter junction is forward biased and the collector-base junction is reverse biased.
To turn on the transistor the base-emitter junction must be forward biased to the point that base-emitter current flows. The collector current that then flows due to transistor action (complex solid-state physics stuff) is the base current multiplied by the current gain of the transistor (Beta or hFE).
Since the forward biased base-emitter junction looks like a diode, the typical base-emitter voltage (Vbe), when the transistor is on, is about 0.65-0.7V.