Background: Polyphenols from Sorbus aucuparia L. (rowanberry) fruits are valuable bioactive compounds, yet their efficient extraction remains a challenge. Ultrasound-assisted extraction (UAE) offers a promising technique to enhance yield, but optimization of parameters is necessary. Methods: UAE was performed using a VC750 processor (20 kHz) at ultrasound intensities of 1.3, 7.65, and 14 W/cm2 in pulsed mode (2 s on, 4 s off). Sonication times of 5, 10, and 15 min (total extraction times: 15, 30, 45 min) and ethanol concentrations of 30%, 60%, and 90% were tested. Selected polyphenols (gallic acid, neochlorogenic acid, chlorogenic acid, vanillic acid, epicatechin, trans-ferulic acid, rutin, quercetin, cinnamic acid) were quantified using HPLC. Response Surface Methodology (RSM) was applied for process optimization. Results: High-quality predictive models were obtained, particularly for neochlorogenic acid. Ethanol concentration exerted the strongest influence on extraction efficiency for most of the studied polyphenols, whereas extraction time showed no significant effect. Conclusions: Ethanol concentration is a key factor in maximizing polyphenol yield from S. aucuparia fruits using UAE. These findings may guide selective extraction strategies for phenolic compounds at early stages of food and nutraceutical processing.