I've come across this symbol in the datasheet (link below) of a transistor for a halogen "electronic transformer" that uses two in a half-bridge operating at about 35KHz. The datasheet mentions nothing special about the transistor, a regular fast-switching bipolar NPN.
Now I understand the presence of the diode, but what is the box connected to all three terminals? I can only think of it as a biasing network, perhaps even resistive. I have searched images on the net for NPN symbol variants and have not seen anything like it.
Can anyone shed light on this?