The Catalan giants, winners of the competition for two years running, added five more goals to their tally in the second leg following last week's rare win at Anoeta.
Sociedad did just about enough to keep themselves in the tie with 10 minutes left to play, but Arda Turan and Denis Suarez - who also scored the opening goal on the night - sealed a place in the last four late on.
Following a rather slack start in which the visitors arguably edged things, Barcelona soon clicked into gear and had an opener when Denis Suarez tucked under Geronimo Rulli.
Sociedad still required two goals to force extra time, and that is the way it remained heading into the interval following a first half lacking any other major openings.
Incredibly, Willian sent a bullet header past Cillessen 20 minutes from time to ensure that Barca still had a little work to do, but any hopes of a shock comeback were short-lived.
Arda Turan came off the bench to slide home a fourth of the night for his side from three yards out, and Denis Suarez then rounded Rulli to add the icing to the cake for defending champions Barcelona.