US media described the margin of victory in Hawaii, current president Barack Obama's home state, as emphatic.
It means the Vermont senator has taken three wins out of three in the states holding votes for their nominations on Saturday, in a major psychological boost to his supporters as he seeks to keep up the pressure on rival Hillary Clinton.
But analysts said the victories had made only a small dent in the significant lead enjoyed by Ms Clinton in terms of numbers of delegates.
After Mr Sanders' two early wins in Washington and Alaska on Saturday, Ms Clinton held a delegate lead of 1,234 to 956, according to an Associated Press analysis, an advantage that expands to 1,703-985 once the superdelegates are included. It takes 2,383 delegates to win.
Democrat presidential candidates
Democrat presidential candidates
1/5 Hillary Clinton
If Americans are fuzzy on the other Democrat runners, they may feel they already know quite enough about Ms Clinton, who has gone from US First Lady to Senator to Secretary of State, navigating serial media maelstroms along the way. It's exhausting to enumerate them (Whitewater, Monica, Benghazi, the email server). She cried in New Hampshire in 2008 yet failed to stave off Barack Obama. Now she's after the nomination again. She has had a lousy campaign so far, yet this remains hers to lose.
2/5 Bernie Sanders
The self-described Democratic Socialist Senator from Vermont is technically an Independent on Capitol Hill but almost always votes with the Democrats. Since jumping into the nomination race, he has stunned probably even himself with the huge crowds he has drawn and his success at raising money from grassroots supporters.
3/5 Marton O'Malley
Mr O'Malley, the Governor of Maryland until the start of this year and before that Mayor of Baltimore, seemed well placed to challenge Ms Clinton. He has a strong record of progressive accomplishments in his state. So far, however, while his speeches are well received, his polling numbers have remained pathetic.
4/5 Lincoln Chafee
Mr Chafee, who shod horses as a young man, was a Republican US Senator for Rhode Island who defied his party and voted against the Iraq War. In 2011, he was elected as the state's governor as an Independent. Now he's running as a Democrat. His pet project? He wants the US to say goodbye to Fahrenheit and go metric.
5/5 Jim Web
Former Virginia Senator Jim Webb has dropped out of the race for the Democratic presidential nomination, although he has hinted that he might still run as an independent.
The Hawaii result nonetheless adds to the landslide wins for Mr Sanders in Washington, where he was leading on 71 per cent in a CNN count late on Saturday, and Alaska, where he had an even greater 80 per cent.
Grinning as he addressed supporters, in Madison, Wisconsin, Mr Sanders said: "I knew that we were going to have a hard time in the Deep South, where people are more conservative. But we knew things were going to improve as we headed West."
Mr Sanders insists there is still a "path to victory" for his campaign. But he needs to win more than 57 per cent of the remaining delegates from primaries and caucuses to have a majority of those delegates by June's end, again according to an AP count.
Washington was the biggest prize at stake on Saturday, with 101 delegates to offer compared to Hawaii's 25 and Alaska's 16, and both candidates had focussed their campaigning there.
Prior to the results coming out, Ms Clinton told supporters in Everett: “We are on the path to the nomination, and I want Washington to be part of how we get there.”Reuse content