State troopers responded to the scene, on southbound I-5 near 375th Street, at about 10:30 a.m. after receiving a report of a serious crash.
A preliminary investigation found that a red Saab convertible was heading south on the freeway, driving erratically and crossing back and forth from one lane to another.
At some point, the driver of the Saab lost control, crossed in front of a semi truck in the right lane and was struck in a crash that severely damaged the vehicle.
The driver, a man in his 40s, was taken to the hospital with life-threatening injuries.
The State Patrol asks anyone who witnessed the crash to contact them.