The 25-year-old lock progressed through the Pro12 club's academy system.
"It's my home region, where I've grown up, and it's an honour to be able to sign up for three more years," said the former Wales Under-20 international.
Ospreys head coach Steve Tandy said: "He doesn't get the credit he deserves outside of our environment, but he's consistent, he's diligent."

Police were called to the gorge, near Blair Atholl, at about 17:50.
Officers have been joined by the fire service, ambulance crews, a helimed and the local mountain rescue team for the search.
A spokesman for Police Scotland said: "There is currently no sign of the individual who is missing."
Lloyd Ashley has committed himself to Ospreys until 2019 by signing a three-year contract extension.
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Emergency services are carrying out a search after a person went missing in the Falls of Bruar in Perthshire.