Use a semicolon to join two closely related clauses. Two sentences may be able to stand on their own, but, for effect, you may choose to join them together with a semicolon. For example: Joe is searching for a teaching job; he has been for months. Both of the clauses are also complete sentences. Choosing a semicolon to join two clauses rather than breaking them into independent sentences can vary the sentence structure of a written work; it's purely a choice of style.
Place a semicolon between listed items that use commas. Typically, a list of items within a sentence could use commas to separate them. The exception is when those items also contain commas, such as cities and states. A semicolon adds more organization to the sentence. For example: Greta found a cheap flight to Fresno, but she has layovers in Cincinnati, Ohio; Austin, Texas; and San Francisco, Calif.
Use a semicolon when you use a conjunctive adverb to join two clauses. Conjunctive adverbs are words such as "however" and "therefore." When you use words like this to join two clauses, you would use a semicolon as well as a comma after the adverb. An example would be this sentence: Ben is always late to work; however, he always stays late to make up the time.