The 20-year-old defender, who made 30 Eredivisie appearances in the 2006-07 season, has signed a five-year contract at the DSB Stadion.

FC Twente had also been interested in signing Koenders but they were put off by the asking price demanded by RKC Waalwijk who successfully negotiated a fee.

Koenders confirmed his delight with the deal and is looking forward to advancing his development as a player in Alkmaar.

"It's fantastic that a club like AZ wants me to join them after only one season of Eredivisie football," Koenders told www.az.nl.

"My performances at RKC have been reasonably good and in Alkmaar I feel I can perfectly develop further. I haven't shown what I am capable of yet by a long way.

"AZ is one of the top Dutch clubs - here I am surrounded by good players, a great coach, a beautiful stadium and I feel when the pre-season starts I will be sharp as a knife."