Radwanska will play sixth seed Serena Williams in Saturday's final after the American beat second seed Victoria Azarenka 6-3 7-6(6).
After a shaky start, third seed Radwanska proved too consistent for her friend Kerber, who had led the first set 3-1 following an early break.
But Radwanska found her range and grew in confidence, forcing the left-handed Kerber to run around court.
"We are really good friends, of course, but on court we're opponents and you're trying everything to make the final," Radwanska said.
"We both were a bit nervous at the beginning, of course. You really want to try your best but sometimes you want it too much and your hands are shaking about, but after that I concentrated on every point."
The 23-year-old broke back to level the first set at 3-3 when eighth seed Kerber netted a forehand and did so again to lead 5-3 before serving out for the set, which she sealed with an ace in under half an hour.
Radwanska broke again early in the second set and although Kerber had one huge chance to level for 3-3, when her opponent put a backhand behind the baseline following a 16-stroke rally, the German wasted it sending a forehand long.
After that, Kerber never looked like getting back into the match and Radwanska sealed victory on her first matchpoint to become only the second Pole to reach a grand slam final.
Jadwiga Jedrzejowska was the runner-up at the 1937 Wimbledon and US Championships and the 1939 French Championships.