Federer – an eight-time winner at his hometown tournament in Basel – required three sets for the third time this week to book his place in the last four.
The world No 3 – who is eyeing a 99th title on the ATP Tour – was unconvincing at times in his 7-6, 4-6, 6-4 quarter-final victory over Frenchman Gilles Simon.
The match was rather gruelling before Federer prevailed after two hours and 34 minutes on court.
Federer will face Russian Daniil Medvedev in the last four later today.
Medvedev has been in exceptional form and has won 37 hard-court matches in 2018.
In doing so, he has won the same amount of matches as Juan Martin del Potro.
Federer is excited about the prospect, which in part is due to a special milestone he will reach.
When asked about his feelings ahead of the semi-finals, Federer said: “I think it will be a tough semis.
“I’m very excited. Apparently it’s my 200th semi-finals on the tour.
“I’m also very excited that it’s here in Basel.”
Federer also paid tribute to the crowd for playing their part throughout his encounter with Simon.
He added: “I really enjoyed it. I think I also showed emotions, I was trying to pump myself up.
“It’s an absolute pleasure playing on home soil with the crowd supporting me so much.
“I think they felt like I was in danger, and it was nice that they were there every step of the way.”