A substrate thermal condtioning apparatus (10) with a chamber (12), a plate (32) located in the chamber (12) and a gas supply (14). The plate (32) has a top heat transfer surface with grooves (42) therealong. A substrate (S) is placed on standoffs (41) of the heat transfer surface and gas is pumped into the chamber (12). The plate (32) is either heated or cooled to change the temperature of the substrate (S). Heat is transferred between the substrate (S) and the plate (32) primarily by gas conduction heating. Because of the grooves (42) in the plate (32), the gas can be very quickly and uniformly distributed and evacuated between the substrate (S) and the heat transfer surface.