Semiana is a comune located in the Province of Pavia within the Lombardy region of northern Italy. It is situated approximately 50 km (31 mi) southwest of Milan and about 35 km (22 mi) west of the city of Pavia.
As of December 31, 2004, the municipality covered an area of 9.9 km² (3.8 sq mi) and had a recorded population of 256 residents.