The Swedish world No. 8 has not dropped a set all week on the Catalan clay and will play either third-seeded Frenchman Jo-Wilfried Tsonga or Thiemo de Bakker of the Netherlands for a place in Sunday's final.
Second seed Soderling saved the only break point he faced against 59th-ranked Schwank, converting three of his four chances, and said he felt his form on the red dust was even better this year than last.
"I had a great (clay) season last year but didn't start so well," Soderling, who lost to world number one Roger Federer in the Roland Garros final, told a news conference.
"Compared with last year I think I am doing better," he said, adding that the knee problem that stopped him competing in last week's Monte Carlo Masters was no longer troubling him.
"The clay makes things easier for the knee and the whole body and I feel good now so fingers crossed." Spanish players continued their impressive performance on clay this year when Fernando Verdasco and David Ferrer both advanced to the last four.
Fifth seed Verdasco, who looked to be feeling the effects of his run to the final at last week's Monte Carlo Masters, edged out Ernests Gulbis of Latvia 6-2, 7-6 and will play Ferrer on Saturday after the eighth seed thumped Brazilian Thomaz Bellucci 6-4, 6-0.
"David is one of the top players, especially on clay," Verdasco told a news conference.
"He is a very tough player, he controls the court very well and it's very hard to knock him off his stride." Rafa Nadal won the title in Barcelona the past five years but withdrew from this year's event to rest ahead of next week's Rome Masters after thrashing Verdasco in the Monte Carlo final.
Ferrer lost to Nadal in the Barcelona title match the past two years and has won 20 of his 22 matches on clay this year, including the title in Acapulco.
