21 year old Hamer has been with Reading since he was 15, last season he played 49 times for Brentford helping them to promotion with the most no. of clean sheets in the division.
Already his loan spells have earned him 115 first team appearances.
Director Of Football Nick Hammond said: "We are delighted that Ben is committing himself to us with this new contract.
"He has a lot of Football League experience under his belt for such a young goalkeeper.
"After his loans he now comes back to us to be very much part of our plans for next season and to contest for the jersey."