The defender has penned new terms to 2027.
Frank said, "This is fantastic news for Brentford and I am incredibly happy that we have Ethan with us for another four years. I'm sure the fans are happy too.
"Ethan has been a rock for us in defence for the past four years.
"He has played a key role in our journey to the top half of the Premier League. He is a top player and a fantastic person."