Nitridation of titanium layer is performed in a high‐pressure (5.9 kg/cm2) ammonium (NH3) ambient. Although the nitridation of titanium surface does not occur at 700 °C in an atmospheric pressure, it does occur at 650 °C in an ammonium pressure of 5.9 kg/cm2. Nitridation temperature can be lowered by 100–150 °C with an increase in ammonium pressure from 2.0 to 5.9 kg/cm2. Thickness of titanium nitride layer increased markedly with increasing ammonium pressure. This is due to the enhancement of the chemical reaction of titanium with ammonium gas by the increase of pressure. The thickness increases with an increase of nitridation temperature. The thickness of the titanium silicide layer formed by the silicidation reaction between titanium and the silicon wafer is reduced with the increase in ammonium pressure.