Senators in the U.S. Senate serve terms of 6 years. However, the re-election period for the Senate is staggered and held in even-numbered years. This is designed so that all members of the Senate are not up for re-election at the same time.
In order to become a U.S. Senator, an individual must be at least 30 years of age. He must be a U.S. citizen and must have been a citizen for at least 9 years. A Senator must also be a resident of the state he intends to represent at the time of his election. Each state has two Senators.