The duo defeated the Croatian-American pairing of Ivan Dodig and Austin Krajicek 6-3, 3-6, 10-7 in the quarterfinals on Friday.
Zieliński and Nys will now face Britain's Jamie Murray and New Zealand's Michael Venus for a place in the championship match at the indoor hard-court tournament in Switzerland.
Zieliński and Nys in May won the men’s doubles at the Italian Open clay-court tournament in Rome.
In January, the two reached the final of the Australian Open men's doubles in Melbourne.
The 2023 Swiss Indoors tournament runs until Sunday.
(gs)
Source: IAR, PAP