Barcelona centre-back Umtiti scored the only goal in St Petersburg on Tuesday, heading home Antoine Griezmann’s corner in the opening minutes of the second half.
With Belgium unable to respond, France secured a place in the final in Moscow, where they will face either Croatia or England.
However, Umtiti has warned Didier Deschamps’ squad not to get too carried away at their progress, insisting they still have a job to do in the Russian capital on Sunday.
“We know that we have to win the next game for this to be a really big achievement. It’s up to us to do the job,” he told BeIN Sports.
“We all worked on this together. I scored, but all our efforts defensively have been rewarded.
“We did the job. It is with this attitude that we can win the World Cup.”
Olivier Giroud praised match-winner Umtiti after his compatriot succeeded where he failed in finding a way to beat Belgium goalkeeper Thibaut Courtois.
The Chelsea striker had six shots in the semi-final but is still waiting for his first goal at the tournament, something he hopes to finally put right in the final.
“I can’t believe it. It was my childhood dream. It is the culmination of an entire career’s work,” Giroud told BeIN Sports.
“For me, I should have scored, but I am so happy for Sam. I hope it will be my go in the final. We are on a little cloud, we hope to stay there, but we will get back to work tomorrow.
“The French can count on us, we will do our absolute best to finish the job.”