Prince Semyon Yurievich of Halshany (Lithuanian: Simonas Juravičius Alšėniškis; died in 1505) was a noble from the Olshanski family in the Grand Duchy of Lithuania.
Olshanski first appeared in politics as Grand Duke's marshal in 1488. Two years later he became starosta of Lutsk and successfully defended Volhynia from the Tatar invasion during the Polish–Ottoman War (1485–1503). He commanded the army in the victorious Battle of Zaslaw in January 1491 and was promoted to Marshal of Volhynia.
When his son-in-law Konstanty Ostrogski was captured in the 1500 Battle of Vedrosha, Olshanski became Great Hetman (commander of the army) of the Grand Duchy of Lithuania. However, he was replaced by Stanislovas Kęsgaila in 1501 or 1502. Jan Litawor Chreptowicz, regent of Nowogródek, was also taken captive at Vedrosha. He was married to Hedwig Olshanska, Semyon's niece, and Olshanski took over Nowogródek. Here as well he was soon replaced by Piotr Hlebowicz. However, he was able to hold the title of starosta of Kremenets until his death in 1505.