Linette, ranked No. 60 by the Women's Tennis Association (WTA), beat Sonmez 6-4, 6-2 on Friday to reach the last four of the WTA 250 event.
The Polish player will next face eighth-seeded Barbora Krejčíková of the Czech Republic for a place in the final.
Linette is the only Polish player competing in the women's singles in 's-Hertogenbosch this year.
In the women's doubles, Poland's Katarzyna Piter and the Czech Republic's Anna Siskova were eliminated in the quarterfinals on Thursday.
They lost 5-7, 6-0, 7-10 to Japan's Eri Hozumi and Taiwan's Fang-Hsien Wu.
The WTA 250 tournament in 's-Hertogenbosch is played on outdoor grass courts and serves as a warm-up event for Wimbledon, which begins later this month.
(gs)
Source: IAR, PAP