Total energy pseudopotential calculations based on norm-conserving optimized pseudopotential and density functional theory (DFT) with generalized gradient approximation (GGA) have been used to study the possible pathway and corresponding energy barrier for the initial dissociative adsorption of silane (SiH4) onto Si(100)-(2 x 2) surface leading to the formation of SiH3 and H adsorbed on Si(100)-(2 x 2) i.e. Si(100)-(2 x 2)(SiH3:H). Our calculated results found that the formation of Si(100)-(2 x 2)(SiH3:H) after the SiHJ initial adsorption onto Si(100)-(2 x 2) surface is energetically favorable. Also the energy barrier, which is calculated to be around 0.72 eV (GGA), occurs clue to the elongation of Si-H within SiH4 accompanying the unbuckling of the buckled Si = Si dimer on Si(100)-(2 x 2) surface. Finally, the reactive sticking coefficient for SiH4 on Si(100)-(2 x 2) is calculated to be around 3 x 10(-6).