The soldier, who has not been named, died after the device detonated in Ayn Issa, north of the IS stronghold Raqqa.
It is the first such death since US special forces deployed in Syria in October 2015.
Meanwhile at least 32 people have been killed in intense Syrian air strikes on rebel-held east Aleppo, monitors say.
The UK-based Syrian Observatory for Human Rights, which monitors casualties, said the attack was one of the heaviest since Syrian forces resumed an offensive on the east earlier this month.
A statement from the anti-IS US-led coalition said the serviceman died on Thursday from wounds sustained in the blast.
Coalition commander Lt Gen Stephen Townsend called the soldier a "hero" and praised those he said were protecting his country from IS's "hateful and brutal ideology".
"On this Thanksgiving, please be thankful that there are service members willing to take up the fight to protect our homeland," he said.
US Defence Secretary Ash Carter said the soldier's death was a "painful reminder of the dangers our men and women in uniform face around the world to keep us safe".
About 300 US special forces personnel have been deployed in Syria to advise an anti-IS alliance of Arab, Kurdish and other fighters, and improve the coalition's targeting of air strikes.
Meanwhile, the Syrian government has intensified its offensive on east Aleppo, monitors and activists say.
"There was an escalation in the evening, with successive bombardments," SOHR director Rami Abdel Rahman told AFP news agency, adding that many people were trapped under rubble.
Five children were reported to be among the dead.
Syrian forces stepped up ground and air attacks on eastern Aleppo in November following a three-week moratorium.
Once Syria's commercial and industrial hub, Aleppo has been divided roughly in two since 2012, with the government controlling the west and rebels the east.
In late September, two weeks after encircling the east and reimposing a siege on its estimated 275,000 residents, the army launched an all-out assault to take full control of the city.
Rebels launched a counter-attack in an attempt to break the siege in late October. But their progress slowed after early gains.

The islands, located off the coast of Cornwall, began the scheme two years ago to protect eggs and baby birds from being eaten by brown rats.
Numbers of manx shearwaters and storm petrels had declined by 25% on St Agnes and Gugh in 25 years.
But colonies are recovering thanks to the rat eradication measures.
Poison placed in an agricultural pipe was positioned in 1,000 locations on the islands in order to kill the vermin.
According to international protocols, the islands could not be officially declared rat-free for two years after the last sign of rat was detected - making them officially free of the rodent on 13 February.
Jaclyn Pearson, from the RSPB Isles of Scilly seabird recovery project, said the seabird population was already starting to recover.
"Straight away we saw results," she said.
"The baiting was done in winter 2013, and in September 2014 we had 10 Manx Shearwater chicks. That's the first time in living memory that chicks have survived and it's clearly because of the removal of the rats.
"We didn't think we would have an uptake of storm petrels so quickly as they hadn't nested on the island for a long time, but we recorded five in 2015.
"So already the results are clear and they're beginning to bounce back."
A questionnaire among residents shows they're delighted with the results, the RSPB said.
The project cost Â£700,000 and was funded by the Heritage Lottery Fund and the European Union.
Wildlife Management International Limited (WMIL) from New Zealand was contracted to carry out the rat removal phase from November to March in "the most humane way".
A US serviceman has been killed by an improvised explosive device while fighting against so-called Islamic State (IS) in Syria, officials say.
[NEXT_CONCEPT]
Two of the Isles of Scilly have been declared "rat free" after a scheme to protect sea birds saw more than 3,000 rodents culled.