The successful growth of ultrathin CoGa on GaAs by MBE is demonstrated. The crystalline quality of the films is verified byinsituRHEED, RBS, and x‐ray rocking curve. Transport studies are performed in the temperature range of 4 to 300 K for layer thickness from 10 to 730 A˚, and all the films are found to be electrically continuous. The Markowitz’s model [Phys. Rev. B15, 3617 (1977)] of the electrical resistivity is applied to analyze the measured data. Finally, the specularly scattering probability of these thin films is studied using Fuchs’ theory [Proc. Cambridge Philos. Soc.34, 100 (1938)].