  We report the performance of a silicon wafer beamsplitter for use for low
$\Delta\nu>0.3 cm^{-1}$ resolution Fourier transform spectroscopy at far
infrared frequencies. We characterize the Si beamsplitter by comparing
throughput spectra measured with it to those measured with the standard Mylar
beamsplitters commonly used in that range. We find that the throughput of the
silicon beamsplitter is substantially greater than that of the Mylar
beamsplitters over most of the IR spectrum, and that they are comparable in
some limited ranges. The 2 mm silicon beamsplitter has an etalon spacing of
about 0.7 cm^{-1}, which interferes with its use for $0.1 cm^{-1}<\Delta\nu <
0.3cm^{-1}$. The average efficiency of the Si beamsplitter is 0.37 compared
with a maximum efficiency of 0.35 for Mylar. The Si is particularly more
efficient in the 100 to 400 cm^{-1} range because of absorption in Mylar.
