A ring segment for a turbine in a gas turbine engine, the ring segment having a backside impingement cavity to collect spent impingement cooling air, and a number of separate impingement chambers spaced around all four edges of the ring segment to provide impingement cooling for the edges. Each impingement chamber is connected to the central impingement cavity by a number of metering and impingement holes to supply cooling air and a number of cooling air exit holes to discharge the cooling air out the sides of the four edges. The trailing edge of the ring segment includes two rows of impingement chambers connected in series.