The biker was heading eastbound on State Route 20 when he tried to take an on-ramp onto southbound I-5, according to Trooper Mark Francis with the Washington State Patrol.
The man was unable to negotiate the curve onto I-5 and went off the road and across both lanes of southbound I-5 before hitting a guardrail.
Francis said the man, a Friday Harbor resident, was wearing a helmet, but it wasn't the type approved by the Department of Transportation.
He died at the scene.
The southbound lanes of I-5 were temporarily closed to traffic as troopers investigated and cleared the area.