I used to work at such a place near london, in kent, .something like "bridge"..
you need to know what is difference between, Thyristor, IGBT, Mosfet,
what uis typical switching frequency..
What is typical switching frequency of a motor (eg the motor that your transistors get used in)
How do you cool a transistor?
What is thermal resistance equation.
What is maximum allowable junction temperature of a fet?
What is maximum voltage withstand.
What is reverse recovery of a diode.
What is a typical trr of your diodes