Already leading 1-0 from the first leg, Barca gave Sociedad a mountain to climb as Denis Suarez finished off a great team move with the only real chance of the first-half before Lionel Messi converted from the penalty spot.
Juanmi and Willian Jose grabbed a pair of consolation goals for the visitors either side of Luis Suarez's third for Barca before Arda Turan and Denis Suarez rounded off the rout.
"After the first goal the space opened up. They had a high line, and if you give the three we have up front space, then they kill you," Denis Suarez told BeIN Sports Spain.
The 28-time winners join Atletico Madrid, Alaves and Celta Vigo, who dumped out Real Madrid on Wednesday, in Friday's semi-final draw.
Barca boss Luis Enrique took no risks with his team selection as all of Messi, Neymar and Luis Suarez started, whilst Gerard Pique returned at the back after being rested for the 4-0 win at Eibar on Sunday.
One moment of magic lit up a first-half otherwise devoid of goalmouth action as after registering his first Barca goal at the weekend, Denis Suarez's purple patch continued.
Samuel Umtiti robbed Xabi Prieto deep inside the Sociedad half and from there Neymar, Messi and Luis Suarez combined to tee up his namesake for a first time finish into the far corner.
"We found it difficult to play out from the back in the first-half," added Enrique.
"In the second-half we took better decisions and we took our chances.
"When the players we have are given space, not just for their quality, but their physical ability, they normally take advantage."
Sociedad had a huge chance to get back into the tie nine minutes into the second period when Jose fired too close to Jasper Cillessen with just the Dutch international to beat from 10 yards out.
And within seconds any lasting hope Sociedad had was gone as Neymar accelerated in behind the visitors' defence and was cynically hacked down by Inigo Martinez with the defender lucky to escape with just a yellow card.
Messi had handed responsibility from the spot to Neymar in each of Barca's last two Cup outings, but stepped up himself to register his 29th goal in just 27 games this season.
Sociedad were briefly given a glimmer of hope when substitute Juanmi took advantage of a glaring gap in the centre of the Barca defence to lob Cillessen.
Barca immediately responded, though, as Messi shrugged off three Sociedad challenges to release Luis Suarez to slot his 20th goal of the season under Geronimo Rulli.
The Basques once again responded as Jose bulleted home a header 17 minutes from time.
Yet, that once again just kicked Barca back up a gear as Turan tapped home Aleix Vidal's cross minutes after replacing Neymar before Messi teed up Denis Suarez for his second of the night.