A semi-colon (;) is used for more than one purpose. Here are some of the things it can be used for:
1. It joins together two separate clauses. EXAMPLE: Mary found an old box in the attic yesterday; it may have belonged to her Father.
2. It can separate a list that contains commas. EXAMPLE: On our holiday we visited the following places: Queensland, Australia; New York, America; Athens, Italy; and London, England.
3.It also seperates two independent clauses. EXAMPLE: I ate some chocolate, a banana, a bag of crisps, and some grapes; still, my favourite thing I ate had to be the chocolate cake.