Mata, who moved to Chelsea in a £26million deal last season, is looking forward to Wembley action.
He said: "This semi-final against Tottenham is huge for us.
"The FA Cup is a special competition and we want to be back at Wembley for the final next month.
"I played there for Spain in November. We killed England but we lost 1-0! Frank Lampard! But what an unbelievable stadium. We've drawn both games against Tottenham in the league this season, so it will not be easy. They have many players at a great level. But so do we.
"Maybe a month ago they were in a better position and we weren't doing so well. Now we're in a good moment and we have to show that at Wembley."