The Spain international, who has four caps to his name, has signed a three-year contract at the Liberty Stadium subject to international clearance and comes in as a direct replacement for Scott Sinclair, who sealed his switch to Manchester City on Friday afternoon.
Hernandez, 27, had voiced his desire to be reunited with Michael Laudrup, having worked with the Swans boss while at Getafe. And he was delighted to put pen to paper after passing his medical, telling the club's official website: "I'm very happy to become a Swansea City player."
He added: "It was my target as soon as I knew there was interest. There were offers from other clubs, but this was the only club I wanted to join."
Hernandez becomes Swansea's eighth summer signing and the fee paid for the wide man just eclipses that paid by the South Wales club to bring midfielder Ki Sung-yueng from Celtic last week.
Hernandez, who scored five times in 40 appearances for Valencia last term, will not be available for Saturday's Barclays Premier League meeting with Sunderland, but is eager to get down to work with Laudrup, one of his heroes.
"I want to thank the club and Michael Laudrup for making me feel like a very important player. Now I want to repay that faith on the football field," he said. "Swansea is a very important football club and will only keep getting better. They were a good side last year and look even better so far this season.
"I watched the game against West Ham on TV last week and they played some good football. I also liked the atmosphere; the fans are good and together with Michael Laudrup's presence it's an exciting package.
"Michael was my idol when I was young. Then I was lucky enough to play under him at Getafe.
"I was a young player at Getafe and I learnt a lot from him. He gave me confidence and I have a lot to thank him for. Now I want to help him at Swansea in return, because he was very important for my career.''