1. One should use a semicolon between closely related independent clauses not joined by a coordinating conjunction.
2. Use a semicolon between independent clauses linked with a conjunctive adverb or transitional expression.
3. A semicolon may be used between independent clauses containing internal punctuation even when a coordinating conjunction links the clauses. 4. Use a semicolon between items in a series containing internal punctuation.
5. Do not use a semicolon to separate a subordinate clause from the rest of the sentence.

On the other hand, I have a friend who has no choice but to use a semicolon because he had to have part of his colon surgically removed.

Don Firth