Silicon‐doped GaAs grown by molecular beam epitaxy has been characterized by Hall measurements, infrared local vibrational mode (LVM) absorption, secondary ion and laser source mass spectroscopy. Highly doped samples with [Si]∼3×1019cm−3show only a low carrier concentration of 8×1017cm−3. LVM spectroscopy shows that SiGadonors are compensated predominantly by [Si‐X] complexes, whereXhas been assigned previously to a gallium vacancy (VGa). Other compensating impurities are not present in the layers at significant concentrations.