The Italian powered to a 6-3, 6-3 win over his fifth-seeded opponent and will next face Alexander Zverev, who saved two match points to beat Daniil Medvedev 2-6, 6-3, 7-6 (5).
Sinner, looking to take advantage of rival Carlos Alcaraz's shock second-round loss to Cameron Norrie, extended his winning streak to 24 successive matches on indoor hard courts.
He will usurp Alcaraz at the top of the rankings by winning the title at the La Defense Arena.
"At the moment I'm not thinking about the ranking," he said.
"It all depends on how I'm playing. We go day by day, every day you have very difficult challenges coming up."
He has now won seven successive matches against the powerful Shelton since losing their first meeting in Shanghai in 2023.
The 24-year-old is targeting his fifth title of the season after last weekend adding the Vienna Open trophy to his Australian Open, Wimbledon and China Open triumphs from earlier in the year.
"I'm happy to be in the situation where I am, tomorrow it's again a very important day but I'm looking forward to it," Sinner added.
The four-time Grand Slam champion wrapped up the first set in just 34 minutes, sealing it with a thumping baseline winner to break Shelton's serve for the second time.
A 22nd consecutive win against American opponents appeared nothing more than a formality for Sinner when he moved 3-1 up in the second set, but Shelton immediately hit back with a break to love before levelling the set to gain a foothold in the match, much to the delight of a packed crowd.
The left-hander's revival did not last long, however, as Sinner broke again in the eighth game.
A deft winner at the net secured a place in his 13th Masters semi-final on his first match point.
Third seed Zverev kept his title defence on track after digging deep in a tense clash with former world number one Medvedev.
Medvedev raced through the first set before losing his rhythm in the second as Zverev forced a decider.
The Russian moved to the brink of victory when leading 5-4 in the third as Zverev made a series of unforced errors on his forehand, but Medvedev passed up two opportunities to secure the win.
Zverev took that momentum into the tiebreak and ended a run of five successive defeats by Medvedev when his opponent fired long and lost any chance of qualifying for this year's ATP Finals.
Bublik battles past De Minaur
Alexander Bublik battled back to defeat Alex de Minaur on Friday and reach the first Masters 1000 semi-final of his career in Paris.
The Kazakh, enjoying his best-ever year, edged a dramatic contest 6-7(5), 6-4, 7-5 to set up a last-four meeting with Felix Auger-Aliassime, who earlier saw off Valentin Vacherot in his quarter-final.
Bublik is still in the race to qualify for next month's Finals in Turin, now competing for the eighth and last berth with Lorenzo Musetti and Auger-Aliassime.
The 28-year-old, who has won four ATP titles this season, also staged a comeback from two sets down against De Minaur at Roland Garros earlier this year en route to the French Open quarter-finals.
He pulled off a similar trick in the French capital on Friday and will be full of confidence before facing Auger-Aliassime on Saturday.
Australian sixth seed De Minaur edged a tight first set, which stayed on serve by reeling off four straight points to recover from 5-3 down in the tie-break.
Bublik hit back, though, grabbing the first break of the match in the third game of the second set to help force a decider.
He saw two break points come and go in the ninth game of the third set, but managed to seal the crucial break in De Minaur's next service game and calmly closed out victory.
Auger-Aliassime ends Vacherot's run
Earlier, Auger-Aliassime cruised past Vacherot to keep his hopes of qualifying for the Finals alive.
The Canadian had come from a set down in all three of his previous matches at the La Defense Arena but eased past surprise Shanghai Masters champion Vacherot 6-2, 6-2.
Auger-Aliassime, targeting his second Masters 1000 final appearance, holds a 3-2 winning head-to-head record over Bublik.
"He (Vacherot) is so confident, and you are kind of scared to be honest," Auger-Aliassime said.
"You are not sure if he has got some magic right now that nobody else has, but he is playing unbelievably.
"I had to be so focused from the start, and this level of intensity from the first game I brought helped ease me into the match, and I played some good tennis."
Vacherot's remarkable run of 10 successive wins in Masters events came to an end. He won the Shanghai tournament earlier this month as a 204th-ranked qualifier.
The Monegasque is still set to break into the world's top 30 after another impressive performance in Paris as a wildcard.
Auger-Aliassime broke in a marathon opening game and went on to dominate the rest of the first set.
Vacherot appeared to be finding his feet early in the second set, but was broken twice in as many service games and slipped 5-2 behind.
He managed to bring up two break points, his first of the match, in the next game, but Auger-Aliassime saved both before successfully holding to finish the job.