The Magpies take on the Saints at St. James' Park on Tuesday, 31st January (kick-off 8pm GMT), with the winners over the two legs progressing to the final at Wembley Stadium.
Tickets for the home leg initially went on sale on Tuesday, 17th January.
And now all tickets for the eagerly-anticipated last four clash on Tyneside have sold out, after the final group of seats were snapped up in an online general sale on Tuesday morning.
To purchase tickets for future United games, visit book.nufc.co.uk.
Official ticket and hotel packages for all Newcastle United home Premier League and cup fixtures are available via club partners SportsBreaks.com. Packages include an official match ticket, plus a minimum one-night stay in a North East hotel, including breakfast.