He was projected to have won 72% of the vote in Washington against 27% for Hillary Clinton.
In Alaska, Bernie Sanders took about 79% of the votes, against 21% for Hillary Clinton.
Results are yet to emerge from Hawaii but initial projections suggest another Bernie Sanders victory.
Washington was the most significant of the three states voting on March 26, with 101 delegates up for grabs. There were 16 delegates on offer in Alaska and 25 in Hawaii.
In spite of his victories, Bernie Sanders faces a struggle to overhaul Hillary Clinton’s overall lead. Going into Saturday’s votes, Hillary Clinton led Bernie Sanders by 1,223 delegates to 920.
When superdelegates who have so far declared their allegiance are included, Hillary Clinton was ahead by 1,692 to 949.
It takes 2,383 delegates to win.
Bernie Sanders tweeted: “Thank you, Alaska! Together we are sending a message that this government belongs to all of us… Washington, thank you for your huge support! It is hard for anybody to deny that our campaign has the momentum.”
The senator earlier told supporters in Wisconsin: “This is what momentum is about. Don’t let anybody tell you we can’t win the nomination or win the general election. We’re going to do both of those things.”
Bernie Sanders had spent the week on the west coast, rallying support among liberals and the left-wing.
He is trying to build on overwhelming victories in last Tuesday’s caucuses in Idaho and Utah.
However, he suffered defeat in Arizona, and although his delegate haul from the three states was 20 higher than Hillary Clinton, he failed to make major inroads into her lead.
Hillary Clinton has pointed out that she has “2.6 million more votes” than Bernie Sanders.
She campaigned less in the three states that voted on March 26, perhaps expecting the defeats, and spent Easter with her family.
This week Hillary Clinton focused on the deadly attacks in Brussels, condemning Republican rivals Donald Trump and Ted Cruz for their “reckless” foreign policies.
Despite March 26 results, the battle will be won and lost in far bigger states still to come. In RealClearPolitics poll averages, Hillary Clinton has the lead over Bernie Sanders by nine percentage points in California, 34 points in New York and 28 in Pennsylvania.
Calculations suggest Bernie Sanders may need to win two-thirds of the remaining delegates – in primaries, caucuses and among so-far uncommitted super-delegates – the unelected officials who can vote for their candidate of choice at the party’s election convention.
There was no voting in the Republican race on March 26.
Donald Trump leads Ted Cruz by 739 delegates to 465, with a total of 1,237 needed to win the Republican nomination, according to AP.
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