Duo Stephen Fitzpatrick and Audun Laading, as well as manager Trevor Engelbrektson, died while travelling to a gig on Wednesday, their record label Heist or Hit has said.
The label described them as "one of the UK's most loved up and coming bands".
Her’s had recently released an album - ‘An Invitation to Her’s’ - on the label, and were touring to support the new music.
They had gained widespread support throughout their early career, with support from BBC 6 Music and BBC Introducing.
Band killed in collision with vehicle going the wrong way
Heist Or Hit said they were killed "in a road accident in the early hours of Wednesday whilst travelling to a show in Santa Ana, California".
Local reports said that four were killed in a crash when a vehicle going the wrong way on Interstate 10 collided with a van carrying three people.
The band had performed in Phoenix, Arizona, on Tuesday and were driving around 350 miles to the next tour date when the crash happened.
Manager Mr Engelbrektson had recently posted a picture of the three of them on Instagram visiting the Grand Canyon to celebrate his birthday.
Posting on their Facebook page on Monday, the band wrote: "It's almost home time for the lads, US tour has gone swimmingly so far. Got a hot sunset date with the Grand Canyon tonight."
Heist or Hit said: “Their energy, vibrancy and talent came to define our label.
“As humans, they were warm, gentle and hilarious. Each time they stopped by the office made for an uplifting experience.
Warm, gentle and hilarious
“To say they were close would be an underestimation of a friendship that was genuinely beautiful to witness; they loved one another like brothers.
“They were in America playing to thousands of adoring fans. Fans they made a point of meeting and spending time with, such was their passion and humbleness.
“The world was at their feet. Everyone here at the label is overwhelmed and distraught.”
The Arizona Department of Public Safety said it was investigating the crash, which killed four people, but could not confirm the identities of those who died.
Fire destroyed much of the evidence
A spokesperson said this delay in the release of information was because almost all evidence of the crash had been lost in the fire, which meant the bodies were unidentifiable.
Her’s was formed at Liverpool university by Mr Fitzpatrick, from Barrow-in-Furness, Cumbria, and Mr Laading, from Norway.
They were nearing the end of their 19 date tour of North America when the crash took place.
The tour had included successful performances at new music festival SXSW in Austin, where they had been filmed by BBC Introducing performing an acoustic set.
Fans have paid tribute to the band.
Michael Craig said: "Absolutely wounded to hear this. Such talented and fun loving people, just gone like that. One of the most genuine and entertaining bands I've seen in a long time. Rest in Peace.
Clarissa Lyle posted: "rest easy to the most precious band I’ve ever watched. Can’t believe I was watching them less than a week ago. Hold onto moments in ur life,, they don’t last forever"
Record shop Rough Trade tweeted: “Absolutely devastating news this morning. Her’s unique debut was an Album of the Month, accompanied by some truly wonderful in-stores. Much loved friends of Rough Trade, a very bright future taken away far far too soon. Thoughts with family, friends and fans.”