The Icelandic frontman is looking to go out to impress for his new club after a sensational season at AZ
The Iceland international has penned a four-year contract with Ajax which will keep him at the club until the summer of 2015.
Neither club have disclosed the transfer fee involved in the deal, but Dutch sources suggest Ajax had to pay €5 million to sign the 21-year-old.
"I’m proud to have signed a contract with Ajax. I’m fast, determined, I can score. I’m looking forward to playing with Ajax," Sigthorsson told the club's official website.
"I’m hoping to become a better player here. I hope I can do great things for the club, win titles, and I want to score more goals than last year."
Sigthorsson, who netted 15 times for AZ last season, is expected to fill in for Mounir El Hamdaoui as the Moroccan striker has been linked with an exit.