We report THz emission of hot-holes inp-type silicon doped with a boron acceptor concentration ofNA=1.5×1015 cm−3.We apply crossed electric(E)and magnetic(B)fields to the crystal cooled to liquid helium temperature. Optical gain is found for field ratiosE/Bin the range0.5–1 kV cm−1 T−1.We calculate optical gain spectra in Si and identify possible laser transitions. ©1998 American Institute of Physics.