Disclaimer: I am biased towards analog so my recommendations tend to be analog-focused.
Behzad Razavi’s book “Fundamentals of Microelectronics”, I find to be a fantastic place to start. It is easy to follow and covers all major concepts in an easily understood manner. The book’s main focus is amplifiers and it is structured in the same way as his UCLA class. His next book, “Design of Analog CMOS Integrated Circuits”, is a great way to build on concepts from his first book. Razavi’s circuits books have received numerous awards and recognition.
Gray/Meyer’s “Analysis and Design for Analog Integrated Circuits” has been widely accepted as the industry standard in analog. Gray/Meyer’s fundamentals will not change despite the fact that the material is a little thick and it is very mathmatical.
Baker’s “CMOS Circuit Design, Simulation, and Layout” is a third book that I often refer to and a great general reference. Baker’s experience at Micron has given him a strong industry focus, making his examples very valuable. If you’re able to, you can also follow his courses at Boise University. I find his lectures to the best online.
We hope that this helps.