Colin Nathaniel Scott, 23, fell into the spring in the Norris Geyser Basin area of the park in north-west Wyoming.
Authorities are now trying to retrieve Mr Scott's body from the spring but have so far been unable to reach it.
Springs in that part of the park, where boiling water runs under thin rock, can see temperatures of up to 93C (199F).
"It's very fragile rock and can be thin as a skiff of ice," said park spokeswoman Charissa Reid.
Park officials say Mr Scott and his sister had strayed some 200 metres (656ft) from a designated walkway. They recommend visitors do not leave trails in hydrothermal areas or approach wildlife.
On Saturday, a 13-year-old boy suffered burns after his father, who was carrying him, slipped into another hot spring in the park. The pair had also reportedly left a path.
Last month, a Canadian tourist put a bison calf into his car boot in Yellowstone as he was worried it looked cold.
The bison was then rejected by its herd, leading it to be put down.
Officials at Yellowstone National Park say a man died after falling into a hot spring, having wandered away from a path.