The 27-year old South African will add his considerable experience and physical presence to the region's second row options after the Ospreys secured an early release from his contract with the Cape Town based side, which had another year to run.
He has 49 Super Rugby appearances to his credit since his Stormers debut in 2010 along with a further 59 games in the Currie Cup, South Africa's premier domestic rugby competition, with Western Province. He was ever present for them throughout the 2012 and 2013 Currie Cup campaigns, where they reached consecutive finals, winning in 2012.
A renowned line out specialist De Kock, who featured for Western Province against the Lions in a feisty clash during the 2009 tour, recorded 14 steals during the 2013 Super Rugby season, a figure second only to All Blacks lock Sam Whitelock of Crusaders.
Steenkamp is 1.97m tall and weighs 112kg.
Speaking about his move to the Ospreys, Steenkamp said:
"Joining the Ospreys is a great opportunity for me and a challenge that I can't wait to get stuck into. The Ospreys are a team with a short but proud history having won the PRO12 four times and talking to the coaches there is an exciting transition going on at the moment that will see them come through the next few seasons stronger than ever.
"I want to be a part of that. Looking around the place and talking to people there really made me excited about signing. Hopefully I'll be able to link up with the squad soon and play a part in helping to make sure the Ospreys remain the best side in Wales as well as one of the best in Europe."
Andrew Millward, Rugby General Manager at the Ospreys, commented:
"This is a significant signing for the region, one that we've been working on for quite some time. We've met with De Kock, spoken to him at great length over a period of time and worked hard to get this deal over the line. He has been to Wales to look around the region and get a feel for what we have to offer and undertake his medical, and he is as excited to be moving to the Ospreys as we are to welcome him.
"He's a natural leader, a combative character, and will be a real asset to the Ospreys. He is a typical South African second row, physical, tough and a natural competitor, who will add to the options available to us in his position. As well as competing for a starting spot he will provide cover for Alun Wyn Jones when he is unavailable and, importantly for us, his presence here all year round will allow us to use his experience to help the ongoing development of the outstanding batch of young locks we have here in the region.
"The likes of Rhodri Hughes, Adam Beard, Rory Thornton and Matthew Dodd will all learn from him. We have worked hard to put ourselves in a position where there are some real prospects coming through the development pathway, but their best interests won't be served by throwing them all in at the deep end before they are ready. Having hard-nosed experience like De Kock around the environment will benefit them and allow them to reach their full potential at the Ospreys."
Steenkamp becomes the ninth new senior signing for the Ospreys this summer while a further 16 current Ospreys have signed new deals during 2014, with a host of promising youngsters also signing up on development contracts.
Guinness PRO12
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