Comment by adrian_b

No. "B" is just the material (for instance "A" = Ge, "B" = Si, "C" = GaAs and related materials).

The letter that encodes the semiconductor material replaced the letter that encoded the voltage or the current used by the heating filament of vacuum tubes.

The material letter has nothing to do with the kind of device.

Examples of silicon diodes: BA (small power rectifier), BB (varicap), BY (high power rectifier), BZ (Zener diode).

It is true that some of the letters that denote kinds of devices have been inherited from the previous nomenclature of European vacuum tubes.

So C, D, F, L, used for low-power/high-power AF/RF bipolar transistors come from the letters used for low-power/high-power triodes/pentodes.

However other letters, like S, U, R, T, used for switching transistors and thyristors (a.k.a. SCRs), were new for the semiconductor device nomenclature.