Choose fruit with a fragrant aroma and flesh that yields a bit when pressed gently. If a peach has cuts or tan spots, or if it's rock-hard or mushy, don't buy it. Color has more to do with variety than ripeness.
Heat grill to medium-low.
Halve and pit peaches; brush both sides with butter.
Place peaches on grill; cover grill, and cook until charred and softened, 4 to 5 minutes per side.