In a method of forming an ohmic layer of a DRAM device, the metal silicide layer between the storage node contact plug and the lower electrode of a capacitor is formed as the ohmic layer by a first heat treatment under a first temperature and an instantaneous second heat treatment under a second temperature higher than the first temperature. Thus, the metal silicide layer has a thermo-stable crystal structure and little or no agglomeration occurs on the metal silicide layer in the high temperature process. Accordingly, the sheet resistance of the ohmic layer may not increase in spite of the subsequent high temperature process.