Senators serve a term of six years. Representatives serve a term of two years. Elections for both fall on even years. The way it is done makes it so that only about 1/3 of senators are up for re-election each time it is a voting year. This is the same for all states in the US, since it is members of Congress, each state does not make their own rules regarding when elections are on and how often their senators and representatives are up for election.