Stephen Street, 32, of Prestatyn, Denbighshire, was told he had taken advantage of a woman in her sleep.
He denied sexual assault but was found guilty by a jury.
He was jailed by Judge David Hale at Mold Crown Court on Thursday and ordered to register with the police as a sex offender for life.
Street had been allowed to sleep on the downstairs sofa at the victim's home following a party, the earlier trial heard.
The victim, a woman from Deeside, told the court she was woken up by a man biting her neck and sexually touching her.
She thought it was her fiance asleep beside her and was "horrified" when she woke up properly to find Street had got into the other side of her bed.
Street's DNA was found on her neck and her DNA was found under the fingernails of his left hand.
A man who sexually assaulted a young woman as she slept in bed with her fiance has been jailed for six years.