The Gunners saw off Everton 4-1 at the Emirates to move into the last four.
Sky Bet duly cut their odds from 3/1 to 6/4 to win what would be their first trophy since taking the same competition in 2005.
Mesut Ozil's early goal was cancelled out by Romelu Lukaku before half time but goals in the last quarter of the game from former Everton hero Mikel Arteta and Olivier Giroud (2) ended the Toffees' hopes.
The big problem for Arsenal now is Manchester City, who remains the odds-on favourites at 5/6 to lift the trophy and add to last weekend's Capital One Cup success.
Arsenal will certainly be keen to avoid City in Sunday's semi-final draw.
The three other quarter-final ties, including City v Wigan in a repeat of last season's final, take place on Sunday.
It's currently 16/1 bar the front two in the betting with Hull, who host Sunderland in the last eight, regarded as third favourites.