Semenyo scored a second goal in two games as City won the first-leg 2-0.
Guardiola said afterwards: "Really good. We were there. First step to reach the final."
On Erling Haaland and Semenyo playing better after halftime, the manager continued: "They were not completely connected. They were not ready to get that ball. Second half they were ready.
"We know Bournemouth did an incredible job with him (Semenyo) and every time the ball arrives to him he always is there."
On Semenyo's second goal being ruled out, Guardiola added: "Four officials and VAR were not able to take the decision, they had to go to the referee. We know how it works and that will make us stronger. It's in that situation how we react.
"It's the semi-finals. We play for a lot to reach the finals. It will make us stronger."