The Swedish world number eight has not dropped a set all week on the Catalan clay and will play unseeded Thiemo de Bakker for a place in Sunday's final.
Dutchman De Bakker, a former junior world number one, took his first top-10 scalp when he upset third-seeded Frenchman Jo-Wilfried Tsonga 6-4 3-6 6-3 in a match briefly interrupted by rain.
The 21-year-old ignored the partisan support from local fans for the flamboyant Tsonga and sealed victory when the erratic world number 10 went long with a forehand return.
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.
Rafa Nadal won the title in Barcelona for the past five years but withdrew from this year's event to rest ahead of next week's Rome Masters after thrashing Verdasco in Monte Carlo.
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