semiconductors are such a great technology. they have single handedly allowed the transition to complex yet cheap and efficient electronic circuits, which is the base of the modern world. and they're also super versatile in other especially optical applications
and all of that only became known really in the early to mid 1900s with the advent of quantum mechanics, which is a necessary base to understand semiconductor behavior
and like this is also a great example of just how useful theoretical physics are - we had semiconductors in the late 1800s, in the form of crystal rectifiers, but it was essentially witchcraft until a theory of operation was found to allow the development of actual devices