Konta was looking to become the first British woman to reach the Wimbledon final since Virginia Wade lifted the trophy in 1977, but she was picked off at crucial times by Williams, who claimed the last of her Wimbledon titles nine years ago.
Williams, who will face Garbine Muguruza in Sunday's final, broke in the 10th game to clinch the first set and then turned the screw on her sixth-seeded opponent, breaking twice more to wrap up the match.
Konta saved two match points before Williams crunched a forehand past the Briton and then twirled in celebration on Centre Court.
At 37 Williams is now the oldest woman in 23 years to reach a Wimbledon final.
"I've played some good tennis in different points of my life. I think it's wonderful to have the opportunity to play well and to be strong and have experience. Experience can either work against you or for you. I like to think it's working for me."
Photo: PHOTOSPORT (Venus Williams).