Alcaraz will face top seed Daniil Medvedev in the semi-finals, after the Russian defeated eighth seed Aslan Karatsev 6-4 6-2 in their quarter-final match.
Medvedev, who is currently ranked world No 1, will be looking to continue his strong form and secure a spot in the final of the China Open.
The semi-finals promise to be exciting matchups, with Sinner taking on Bu and Alcaraz facing off against Medvedev.
Tennis fans can look forward to some thrilling tennis as these talented players battle it out for a place in the final.