The semicolon is used to separate independent clauses in specific situations. It also separates a series of items which contain internal punctuation.
1. Use a semicolon between independent clauses when the clauses are closely related in meaning and when there is no coordinating conjunction between them.
When you come to London, you will stay with me; I wouldn't have it otherwise.
Be careful and drive defensively; you'll be glad you did.
2. Use a semicolon between independent clauses linked with a transitional expression.
|after all||even so||in fact|
|as a matter of fact||for example||in other words|
|as a result||for instance||in the first place|
|at any rate||in addition||on the contrary|
|at the same time||in conclusion||on the other hand|
The cook's specialty is broiled salmon; however, tonight it's not available.
That's a difficult question; in other words, I'm not going to answer it.
The man pleaded innocent; his face, however, looked as guilty as sin.
The hike will be difficult to complete, dangerous to attempt, frightening for most of us, and long; and in spite of her reassurances, I don't even think we should go.
3. Use a semicolon between items in a series containing internal punctuation.
We visited Washington, D.C., in the fall; Downer's Grove, Illinois, in the spring; and Cooperstown, New York, in the middle of a very hot summer.
The population of my hometown in 1762 was 4,123; in 1790, 7,921; and in 1998, 42,380.