基极总是比发射极和集电极薄得多。

The base region is always very much narrower than the emitter or collector regions .

特点：基极-发射极间内置电阻，高电压。

Features: Built-in resistor at B-E, high voltage.

我们取发射极基极电阻的典型值为250欧姆左右。

We shall take the typical emitter-to-base resistance as about 250 ohms.