American Idol star Adam Lambert has fired back at criticism he received from Gene Simmons, calling the KISS star "obnoxious" and "a d**k".

Simmons criticised Lambert for 'coming out' as a gay man shortly after Idol wrapped in May, claiming the big reveal would hurt his career.

Lambert ended weeks of speculation by declaring his sexuality just days after he lost the 2009 show finale to Kris Allen and Simmons insisted he should have kept the information to himself, because his homosexuality will now overshadow everything he ever does.

The KISS star said, "He killed his career because now the conversation is not about his talent but about his sexual preference. He's done."

But, as he prepares to debut his first album, Lambert begs to differ - blasting Simmons in a new Rolling Stone interview.

He rages, "He's (Simmons) obnoxious, and what a hypocrite - all he talks about is his sex life.

"He was being a d**k - and he's not the greatest singer."