The Liverpool icon singled out a surprise Gunner for praise on social media.
Alexis Sanchez scored Arsenal's extra-time winner against the Championship side but it was defender Paulista's role during the goal Carragher was most impressed with.
The Liverpool icon would have been watching closely - the Reds face Aston Villa in the other cup semi-final at Wembley on Sunday afternoon and his former side will have painful memories of playing Arsenal lately.
Sanchez 2-1 Arsenal but the role of Gabriel was excellent in dealing with the Reading counter attack just before the goal.— Jamie Carragher (@Carra23) April 18, 2015
The Gunners beat Liverpool 4-1 at the Emirates Stadium when the two sides last met in the Premier League.
And Brendan Rodgers' men will most likely struggle to break down an Arsenal defence that contains the 'excellent' Gabriel - especially if Daniel Sturridge is injured and they have to field a forward who is not a natural striker.
Liverpool, though, will be given encouragement if Arsene Wenger opts to start Wojciech Szczesny once again. The Arsenal goalkeeper has become unreliable of late and erred for Reading's goal.
First, however, the Reds have to overcome Aston Villa. Arsenal - thanks to Sanchez, Gabriel and co - have done their part...