The 22-year-old will face either second seed Andy Murray or unseeded Fernando Verdasco for a place in the final. Janowicz, the 24th seed, fired 30 aces and 58 winners before breaking down in tears and even exchanging shirts with his Davis Cup teammate.
“I’m just really happy. I didn’t expect I can go that far in a Grand Slam here at Wimbledon,” he said. “Really I have not many words to say right now. I’m just really happy and it doesn’t matter if I’m the first or second from Poland. It’s my first semi-final and that’s all that matters.”
Janowicz had already exceeded his best Grand Slam performance by making the quarter-finals and has capitalised on the shock exits of Roger Federer, Rafael Nadal and Jo-Wilfried Tsonga from his half of the draw.
Kubot, the 31-year-old World No 130, was bidding to become the lowest-ranked semi-finalist at Wimbledon since Vladimir Voltchkov made the last-four as a 237-ranked qualifier in 2000.
Victory for Janowicz will see him rise to at least 17 in the rankings next week which would be a career high for the 2.03m giant from Lodz.