Roth died late Saturday while visiting his daughter in Washington, friends told the Wilmington, Del., News Journal.
Ross represented the state in Congress for more than 30 years, becoming the longest-running statewide-elected official in Delaware history, the newspaper said.
He lost his bid for a sixth six-year term in the 2000 election to Democrat Tom Carper. During the campaign, the then 79-year-old claimed his age was an asset.
"My background and experience enables me to make a significant contribution," he said.
Nationally, Roth was best known as co-author of the 1981 Kemp-Roth tax cut and creator of the Roth IRA tax-free savings account.
Roth made it his personal goal to reduce government waste and uncovered the Pentagon's infamous $9,600 wrench and $640 toilet seat purchases.