Muller was on the scoresheet for Die Mannschaft in Belo Horizonte on Tuesday as they thrashed the hosts to reach Sunday's final.
"It's an indescribable feeling," he told FIFA.com. "We got off to a great start and when you're 5-0 up at half time against Brazil in Brazil then you know it's something special.
"We need to let this all sink in now and then shift our focus to the final. We want to win the trophy and we're going to give everything to make that happen."
Germany will face the winner of tonight's other semi-final between Argentina and the Netherlands in the final.