Low temperature growth of GaAs not only provides useful semi-insulating layers in a variety of devices, but also is interesting from a materials and crystal growth point of view. In this work we have utilized an in situ spectroscopic ellipsometer having 44 wavelength regions in the range 4000-8000 Angstrom to monitor the low temperature growth of GaAs. Several different regions of growth have been observed, in agreement with earlier studies utilizing single wavelength ellipsometry. An initial region of homogeneous growth is followed by regions of material that exhibit varying optical properties. The complex refractive index of the epitaxial LT-GaAs films have been extracted from the real-time data acquired during the homogenous growth region. Ex situ characterization of these films was performed using high-resolution x-ray diffraction to determine the excess As concentration. Films in which the low temperature growth was stopped within the homogeneous growth regime have been characterized with a multiwavelength variable angle ellipsometer, and the complex refractive index of these films in the range 4000-17000 Angstrom have been extracted.