The South African-born flyer enjoyed an impressive first full season with the Welsh outfit, notching up eight tries in 24 appearances, including the RaboDirect PRO12 Try of the Season.
"Hanno has enjoyed a great season and has really shown what a talent he is. It's great that we can call on his services for another two seasons. If he continues to work hard and shows the attitude and desire to improve his all round game that we've seen from him since he joined the group, he could have a very bright future with the Ospreys," head coach Steve Tandy told Ospreys' official website.
The 21-year-old revealed his joy at having secured his stay at Liberty Stadium.
"I'm very happy. The Ospreys are the best team in Wales and I'm really happy to be a part of the organisation. I feel at home here, everybody has made very welcome and this is my region so I'm happy that I can continue playing for the Ospreys," he said.
"I've been given some chances this season and I think I've taken them the best I can. It's great to be playing and training with top class players, Wales internationals and Lions, it's been an absolutely amazing year for me. It's nice to be in a squad with so many top class players that I can learn off.
"I'm really excited about the way the team is developing, we seem to be growing every day, every week. It's good to be finishing off the season with a final, we have worked hard to get there and now we have to make sure we don't let anybody down."
While born in the South African town of Krugersdorp, Dirksen moved to the USA with his family in 2006 and has turned out for the Eagles at age-group level.
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