US Election 2016: Sanders wins Washington, Alaska and Hawaii
The biggest prize was Washington state, but Mr Sanders also won in Alaska and Hawaii, boosting his campaign.
He took at least 70% of the vote in all three states.
Mr Sanders thanked his supporters and said his "campaign has the momentum", but he still faces a tough task to overhaul Mrs Clinton.
After Saturday's caucuses, she leads Mr Sanders by 1,243 delegates to 975, the Associated Press count shows.
When superdelegates - party officials who can support either candidate - who have so far declared their allegiance are included, Mrs Clinton is ahead by 1,712 to 1,004 in the race to reach 2,383 delegates.
Bigger battles ahead
Washington was the most significant of the three states voting on Saturday, with 101 delegates up for grabs. There were 16 delegates on offer in Alaska and 25 in Hawaii.
Mr Sanders won 73% of the vote in Washington against 27% for Mrs Clinton, AP reports.
He won a massive 82% of the vote in Alaska, against 18% for Mrs Clinton. In the Hawaii caucus, Mr Sanders won by 70% to 30%.
In total, Mr Sanders won 55 delegates and Mrs Clinton secured 20. More delegates from Washington will be allocated in coming weeks.