Provided is a method of manufacturing a semiconductor device with enhanced electrical characteristics. The method includes disposing a substrate on a substrate support in a process chamber, pre-heating the substrate on the substrate support adjusted to a temperature from 300 to 400.degree. C. for 60 seconds or more, forming a silicon protective layer on the substrate by supplying a silicon source gas into the process chamber and heating the substrate on the substrate support adjusted to a temperature from 300 to 400.degree. C. for 10 seconds or more, and forming a tungsten layer on the silicon protective layer.