The accident happened around 5:15 a.m. on Salem Church Road near Old Baltimore Pike.
49-year-old Troy Schroeder of Landenberg, Pennsylvania was riding north when he veered off into the southbound lanes, police say.
In an attempt to return the motorcycle to the correct lane he struck the median, flipped over and was ejected from his bike.
Schroeder was taken by ambulance to Christiana Hospital with a head injury.
He is listed in critical condition.
Delaware State Police are investigating the crash.