World number 38 Vondrousova beat Croatian 31st seed Petra Martic 7-6 (7/1), 7-5 to become the first teenager into the semi-finals since eventual champion Jelena Ostapenko in 2017.
Konta became the first British woman in 36 years to reach the semi-finals when she defeated Sloane Stephens of the United States 6-1, 6-4.
Vondrousova had to dig deep to reach her maiden semi-final.
She trailed 3-5 in the first set and gave up a 5-2 lead in the second set, squandering three match points in the process before she held her nerve to win.
Her victory over Martic came despite having lost all four of their previous meetings including at the Australian Open in January and in the final of the clay court event in Istanbul in April.
"She had beaten me four times but I think Roland Garros must be my lucky place," said the Czech.
She shares a 1-1 head-to-head record with Konta but the Briton won their last meeting on clay in the Italian Open quarter-finals on the eve of Roland Garros.