The ionization energy of lithium as an impurity in single-crystal silicon has recently been determined by optical means to be dependent upon the amount of oxygen in the silicon. It was found that for float-zone crystals, having a relatively low oxygen content (less than 10¹⁶ cm⁻³), the ionization energy was about 32 meV, whereas for a pulled-crucible crystal, having a higher oxygen concentration (approximately 10¹⁸ cm⁻³), the ionization energy was 39 meV. Previous measurements by means of Hall effect studies had indicated that the ionization energy in a pulled crucible sample was about 33 meV which seemed to agree with the optical float-zone value. In an attempt to clarify the situation, Hall effect measurements were made on pulled-crucible and float-zone silicon samples containing lithium as an impurity, and ionization energies were calculated. It was found that this new Hall effect data seemed to show the same dependency on oxygen content as the optical data had shown with the ionization energy, being 37 meV for the pulled crucible sample and 29.5 meV for the float-zone / Master of Science