Illinois State Police said the 68-year-old Chicago man was shot in the face on the northbound Dan Ryan near 95th Street around 11:50 p.m. Thursday.
Good Samaritans saw the driver weaving from left to right after the shooting. They called for help. The driver was rushed to Advocate Christ Medical Center, where he is listed in critical condition.
There was no one else in the semi with him.
State troopers shut down the northbound Dan Ryan between 95th and 87th for hours to search the pavement for bullet casings. All lanes reopened around 4:35 a.m. Friday.
People who live nearby said they couldn't believe they were hearing about yet another expressway shooting.
"It's dumb. Senseless. You gonna shoot somebody cause they either cut you off or something. Then you gonna kill somebody else and more than one person gonna die. It's just dumb," a neighbor said.
Police are searching for the gunman. They did not give a description of the suspect or the suspect's vehicle.