This falls more into the electronics domain, which I know is sometimes put under the "semiconductor" bucket, but in universities usually has its own domain ("microelectronics" in my day). It's a lot more focused on the circuit/high frequency model of the transistor, and builds up form it.

Semiconductor theory is more about the transistor and everything below it: Starting from quantum mechanics and statistical mechanics, derive the equations of electron/hole transport in a doped semiconductor, how the material's band structure impacts current flow, etc. The derivation of the transistor equations is often the end point.