We have developed a new design for a cryogenically cooled monochromator employing a thin‐crystal strategy which is capable of handling the central‐cone power of the advanced photon source’s undulator A at machine currents up to 300 mA. The key to the proposed design is to machine two opposing narrow channels in a large, indirectly cooled block of Si crystal, leaving a thin, ∼0.6‐mm‐thick strip of Si. The thin section absorbs only a fraction of the incident beam power so that the operating temperatures of the crystal are in the range where Si has both a very high thermal conductivity and a very small or slightly negative thermal expansion coefficient. The fact that the crystal is operated in the negative range of thermal expansion means that the crystal surface illuminated by the x‐ray beam is always under tension and therefore will not buckle.