In an ohmic layer and methods of forming the ohmic layer, a gate structure including the ohmic layer and a metal wiring having the ohmic layer, the ohmic layer is formed using tungsten silicide that includes tungsten and silicon with an atomic ratio within a range of about 1:5 to about 1:15. The tungsten silicide may be obtained in a chamber using a reaction gas including a tungsten source gas and a silicon source gas by a partial pressure ratio within a range of about 1.0:25.0 to about 1.0:160.0. The reaction gas may have a partial pressure within a range of about 2.05 percent to about 30.0 percent of a total internal pressure of the chamber. When the ohmic layer is employed for a conductive structure, such as a gate structure or a metal wiring, the conductive structure may have a reduced resistance.