Ferrero, the second seed, need just 72 minutes to reach his first semifinal at the claycourt tournament, easing past Tommy Haas of Germany, the fifth seed, 6-3, 6-1.
The fourth-seeded Henman also advanced to the final four at Monte Carlo for the first time, rallying for a 2-6, 6-4, 7-6 (7-4) triumph over the eighth-seeded Thomas Johansson of Sweden.
Ferrero broke Haas' serve in the match's opening game. Trailing, 3-2, the Spaniard reeled off eight games to open a 4-0 cushion in the second set and the German did not threaten again.
"Before this tournament, I was injured. So I couldn't play the hardcourt season in the United States or in Estoril," Ferrero said. "Now, I'm pleased to be able to reach the semifinals and hopefully go on to become the champion."
Ferrero is trying to reach his third consecutive claycourt final in a Tennis Masters Series event. In May 2001, he won the Rome title and was the runner-up to compatriot Albert Portas at Hamburg.
The British No. 1, Henman defeated Johansson, the Australian Open champion, for the fourth time in their five career meetings. The Swede's lone success came in the quarterfinals at Dubai in last month.
Henman became the first British player in 27 years to move into the semifinals at Monte Carlo. In 1975, John Lloyd lost to Bob Hewitt in the last four at Monte Carlo.
"It's pretty good going, but I'm not finished yet," Henman said. "I felt like the level of challenge went up today against Johansson, and tomorrow it will probably go up another level against Moya. He's a world class player at the best of times and on clay he's even better."
Henman also reached the quarterfinals here last year. Grosjean reached the Monte Carlo semifinals for the second consecutive year with a 6-4, 6-2 victory over Spain's Albert Costa.