Abstract: Two thin epitaxial GaAs films on Ge substrates were characterized by photoluminescence (PL), contactless electroreflectance (CER), and piezoreflectance (PzR) techniques. The GaAs films containing antiphase domains (APDs) and those APD free were grown at 650 ° C by metal organic vapor phase epitaxy. The PL intensity of the APD-containing film is four orders of magnitude lower than that of the APD-free sample. The reduction in intensity is due to the electrically active Ga–Ga and As–As bonds at the boundaries between the different APDs. The electric fields deduced from Franz–Keldysh oscillations of the CER spectra were used to determine the net carrier concentration of the GaAs films. In addition, the conduction to light-hole band transitions and the conduction to heavy-hole band transitions that originated from strain induced valence band splitting in GaAs thin films were observed and identified through a comparison of the relative intensities of light- and heavy-hole related features in the PzR and CER spectra. The results demonstrate that PL, CER, and PzR are useful nondestructive tools to characterize thin epitaxial GaAs films on Ge substrates.