The predicted half-metallicity of Co2FeSi in combination with its high Curie temperature of above 980 K makes this Heusler alloy interesting for spinelectronics. Thin Co2FeSi films are grown by molecular-beam epitaxy on GaAs (001) with a close lattice match. We present a study of point-contact measurements on different films, varying in thickness between 18 nm and 48 nm and in substrate temperature during deposition between 100 °C and 300 °C. Transport spin polarizations at the Fermi level are determined from differential conductance curves obtained by point-contact Andreev-reflection spectroscopy. A maximum transport spin polarization of about 60% is measured for a 18 nm thin Co2FeSi film grown at 200 °C.