is there any website which explain the concepts of semiconductors with simple circuits.....?
It depends a lot on how much you understand already. Class notes provided by your lecturer or his/her recommended textbook will be designed to match what you need to know. A library may be able to lend a book, (so no cost), on electronics/ semiconductors to explain basic concepts.
Or you could try these sites.
Or Google around until you can find something that suits.
Try to write down a set of questions covering what aspect you want to refresh and ask a tutor or lecturer to guide you. He/she will be pleased you are trying to improve.
Regards - Ian