That will be followed by the 150th-ranked Raducanu against No. 17 seed Maria Sakkari of Greece. Raducanu is the first female qualifier to get to the final four at the U.S. Open in the professional era, which began in 1968.
None of the four women remaining in the tournament ever has played in a Grand Slam final.
Thursday's schedule also includes the men's doubles semifinals. It is raining at Flushing Meadows and the first doubles semifinal has started at Louis Armstrong Stadium with the retractable roof shut. Steve Johnson and Sam Querrey are facing Rajeev Ram and Joe Salisbury.
Matches in the wheelchair and junior competition that were scheduled to start at noon are being delayed because of the rain, which is forecast for much of the afternoon and early evening.
Ashe and Armstrong are the only two courts with roofs.