Go to Microelectronic Devices and Circuits (MIT Open Course Ware OCW, Lecture Notes.)
These lecture notes discuss the foundations of semiconductor physics and devices like MOSFET and BJT transistors. In addition to the devices that are covered, the electronic circuits that can be built with these devices are also discussed and analysed. But for a more comprehensive discussion of electronic circuits you should better look at Sedra / Smith or some other resource on the analysis and design of electronic circuits.
A nice feature is the "What did we learn today" page at the end of each lecture, that provides a good summary of the key concecpts of the lecture.In addition to the lectures, you might also have a look at the Assignements and Exams (see the menu at the left side of the page) to test your knowledge.
Wise Warthog Site Overview:
General: Forums, Tips on how to seek Advice
Practical Electronics: Books and Other General Resources, Troubleshooting, Introductions to Oscilloscopes, Breadboarding and Prototyping
Foundations: Basic Linear Circuit Analysis, Analysis and Design of Electronic Circuits, Introductions to Analog IC Design, Circuit Simulation with SPICE
Devices: General Op Amp Resources, Op Amp Applications, Resistors, Capacitors, Diodes, Bipolar Junction Transistors
Application Notes: Analog Devices Seminar Notes, Columns and App Notes by Bob Pease, App Notes by Jim Williams, E-books and App Notes from Texas Instruments
Mathematics: Complex Numbers, Calculus, Mathematics for Physics and Engineering
Wise Warthog - Learning Resources
for Analog Electronics and more