American Carson Storch put down the marker early on with a superb score of 85.66 as 2019 Red Bull Joyride champion Emil Johansson of Sweden also impressed on his Red Bull Rampage debut with a 79.
Semenuk, though, looked in the zone and the 2008 and 2016 champion pulled off a brilliant first run of 92.33 that included an opposite 360 and backflip.
Briton Brendan Fairclough was a big fan favourite in 2018 and he had the crowd on their feet again with an excellent highly technical run of 87.66 that featured a breathtaking backflip over a canyon.
Polish star Szymon Godziek, two-time American winner Kyle Strait and compatriot Tyler McCaul all reeled off impressive runs in the 80s with Canadian Tom van Steenbergen building on his 2018 Best Trick award with an insane run full of big backflip drops to post 89.66.
Rheeder was unusually messy in his opening run to score 84.33, but made amends in the second run with a score of 91 despite the wind starting to pick up.
Fairclough had the chance to improve on his first run, but opted instead to pay tribute to Canadian Jordie Lunn, who sadly passed away earlier this month in a Mexican bike crash, with some course push-ups.
Van Steenbergen decided not to take his second run meaning that he finished third with Rheeder second and Semenuk able to go down his second run safe in the knowledge that he had wrapped up his third Red Bull Rampage title to match compatriot Kurt Sorge.
The 28-year-old said: "Obviously last year didn't go very well. We had a good line, I didn't rush and I got something good down. Still nerve-racking, but I was feeling it. I don't think people realise how much Jordie did for me when I was young. He was a best friend."
- Rheeder, 26, added: "I broke the ice on round one and luckily I didn't get affected by the wind. The season is over now and I am so happy to be in one piece."
RED BULL RAMPAGE 2019 FINAL RESULTS
- Brandon Semenuk (CAN) - 92.33
- Brett Rheeder (CAN) - 91.00
- Tom van Steenbergen (CAN) - 89.66
- Brendan Fairclough (GBR) - 87.66
- Tyler McCaul (USA) - 87.00
- Szymon Godziek (POL) -86.66
- Ethan Nell (USA) - 86.00
- Carson Storch (USA) - 85.66
- Kyle Strait (USA) - 83.33
- Vincent Tupin (FRA) - 81.33
- Reed Boggs (USA) - 80.00
- Emil Johansson (SWE) - 79.00
- Graham Agassiz (CAN) - 76.33
- Thomas Genon (BEL) - 74.00
- Reece Wallace (CAN) - 72.00
- DJ Brandt (USA) - 70.33
- Andreu Lacondeguy (SPN) - 52.33
- Kurt Sorge (CAN) - 51.66
- Bienvenido Agua Alba (SPA) - 45.33
- Cam Zink (USA) - 36.66