The electrical resistivity and Hall effect measurements have been made on vacuum evaporated Bi90 Sb10 alloy films of various thickness (350 A to 4500 A), in the temperature range of 77 to 510 K. As observed earlier, the alloy system behaves like a semiconductor, but with a band gap quite higher than previously reported for bulk single crystals. Also a kind of intergrain barrier is found in these films. The activation energy of these barriers is found to decrease with increasing film thickness and substrate temperature. This trend agrees with the earlier observations in other materials and also in the same alloy system. The higher band gaps in these films are attributed to quantum size effect and high dislocation density in these films. The decrease in the inter-grain barrier activation energy with increasing thickness and substrate temperature has been attributed to increased grain size of the films. © 1981.