The semicolon ( ; ) is an important punctuation mark
in English and has several uses. One is in connecting
sentences with closely related ideas. Another is in lists
of items that contain commas. A third is with a special
group of connecting words called conjunctive adverbs.

Conjunctive adverbs include connecting words such as
however, therefore, besides, consequently, nevertheless,
in addition, accordingly, and otherwise; conjunctive
adverbs (which are sometimes also called sentence
connectors) are especially common in serious business,
technical, and academic writing.

When sentences are connected by using conjunctive
adverbs, the semicolon comes at the end of the first
sentence; the conjunctive adverb (with a small first
letter, not a capital) comes next andis usually
followed by a comma.

Examples:

Sheila might have been sick and unable to
come to work; however, I suspect that she
took the day off and went shopping.

We're expected to do all the assigned work;
in addition, we're required to read and report
on three books that we can choose ourselves.

The last three shipments were damaged when
they were received; consequently, all new
shipments will be inspected just before they
leave the factory.

Maurice found the work very difficult and was
often tempted to quit; nevertheless, he kept on
trying and eventually did quite well on it.

Special Note:

Periods can be used with conjunctive adverbs instead
of semicolons. If periods are used, the conjunctive
adverbs begin with a capital letter, not a small one:

She was extremely tired. However, she finished
her assignment. / She was extremely tired; however,
she finished her assignment.