Schottky diode like BJT symbol
You need to understand three things in order to understand a Schottky transistor.


In an ordinary BJT, the saturation state collector-emitter voltage falls below or equal to 0.2&nbsp;V.
In an ordinary BJT, the base-emitter voltage must be equal to or above 0.8&nbsp;V.
The saturation state voltage drop of a Schottky diode is around 0.3&nbsp;V.


Now, if we consider all this information together; a Schottky transistor cannot enter into saturation state, because, voltage drop on the diode (0.3&nbsp;V) added to the voltage drop on the transistor (0.2&nbsp;V) doesn't reach the required saturation base-emitter voltage of the transistor.

Why do we need a transistor like this?
One of the biggest disadvantages of BJT is that it gets out of the saturation state very slowly. This causes a low switching speed. But, if it doesn't enter into the saturation state, it can be turned off much faster. That's the reason why the Schottky transistor is used.