Several high‐resolution HgI2x‐ray detectors have been made from single crystals grown from the vapor phase. Hole and electron transport properties and detector electrical characteristics are described. Measured mobility‐lifetime product for electrons is 8×10−5cm2/V with a &mgr;eof 3 cm2/V sec. The mean energy per electron‐hole pair is 4.33 eV at 122 keV. Detectors up to 1 mm3are described, and a resolution as low as 850 eV at 300 °K in air has been obtained for 5.9‐keV x rays, which suggests possible x‐ray flourescence detection applications.