Defending champion Serena Williams thrashed Russia's Elena Vesnina 6-2 6-0 to set up a potential fifth Wimbledon final against older sister Venus.
Six-time champion Serena, 34, simply had too much firepower for her unseeded opponent, winning in 48 minutes.
Five-time winner Venus, 36, plays Australian Open champion Angelique Kerber in Thursday's second semi-final.
Serena, 34, has won three of the four all-Williams finals, with the most recent coming in 2009.
Vesnina, a two-time Grand Slam champion in doubles, looked overawed from the outset, losing the first four games.
The world number 50, playing in her first Grand Slam singles semi-final, rallied but still lost the first set in 28 minutes.