NO 2 exposure drastically increases the hole concentration on the surface of hydrogen (H)-terminated diamond. When the NO 2 gas concentration is higher than 300ppm, the saturated hole sheet concentration p s stays the same. Therefore, the p s value is regarded as the high limit of the concentration of holes on H-terminated diamond surface, p s,max . In this work, we compared p s,max , mobility μ, and sheet resistance R s for (100), (110), and (111) H-terminated surfaces of chemical-vapor-deposited single-crystal diamond. On (110), (111), (100) surfaces, the p s,max values are 1.717×10 14 and 1.512×10 14 cm −2 , and 0.981×10 14 , respectively. This result supports the first-principle calculations: the hole concentration depends on the energy difference between the valence band maximum and the unoccupied orbitals of adsorbent NO 2 molecules. We have achieved R s of 719.3 Ω/sq (p s =1.456×10 14 cm −2 and μ=59.6 cm 2 V −1 s −1 ), the lowest reported so far, on (111) surfaces under 20,000-ppm NO 2 atmosphere.