The present invention relates to a method of manufacturing a semiconductor device, which is capable of effectively removing a WO.sub.3 film generated on a tungsten silicide during contact hole etch that opens a gate electrode including the tungsten silicide as its top film by selectively etching a interlayer insulating film. The WO.sub.3 film is removed by a washing process using an alkaline solution such as TMAH(tetra-methyl-ammonium-hydroxide) or NH.sub.4 OH solution. The effective removal of the WO.sub.3 film reduces the contact resistance between a conductive material layer to be formed in he contact hole by a later process and the gate electrode, thereby improving the operative characteristics of the semiconductor device. TMAH solution used in the washing process has a high selectivity of WO.sub.3 film relative to a thermal oxide film or a BPSG film that is generally used as the interlayer insulating film. Thus, the present invention is capable of minimizing the damage of the side parts of the interlayer insulating film during the washing process after contact etching.