The 2000 United States Senate election in Delaware was held on November 7, 2000, in conjunction with the 2000 U.S. presidential election, other elections to the United States Senate in other states, as well as elections to the United States House of Representatives, and various state and local elections. Incumbent Republican U.S. Senator William Roth ran for re-election to a sixth term, but he was defeated by outgoing Democratic Governor Tom Carper. Carper subsequently became the first Democrat to hold this seat since 1947. It was also the first time since 1943 that both seats were held by Democrats.

William Victor Roth Jr. was an American lawyer and politician from Wilmington, Delaware. He was a veteran of World War II and a member of the Republican Party. He served from 1967 to 1970 as the lone U.S. Representative from Delaware and from 1971 to 2001 as a U.S. Senator from Delaware. He is the most recent Republican to have served as a U.S. Senator from Delaware.