A list of the Class I Senators who were elected in November 2014 can be found on the website of the U.S. Senate. These senators' terms expire in January 2021.
Article I Section 3 of the U.S. Constitution mandates that the U.S. Senate should be divided into three classes, elected every two years. Class I was elected in 2014. The classes are roughly equal in number of senators. As new seats are added to the senate, the new seats are distributed evenly among the classes to maintain roughly equal size. When the first congress was elected, Class I senators sat for only two years before their terms expired. Class II senators sat for four years, while Class III senators sat for the full six-year term.