"Cities like Hanoi have seen a search and booking rate increase of up to 298%, Da Nang 439%, and Ho Chi Minh City 219%," Expedia says.
"These searches prove there's more to the world than stereotypical destinations that people go to every year," it added.
Last year the U.S. accounted for the second highest number of visitors to Vietnam: 215,000.
More than 200,000 U.S. arrivals came in the first quarter, the third largest groups after those from South Korea and China.
U.S. citizens are only offered a one-month, single-entry e-visa by Vietnam.