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Interfacial roughness in heterostructures critically degrade the optical and electrical properties of the devices fabricated with III‐V semiconductor compounds. Experimental work on the surface roughening processes during MBE growth by monitoring the reflection high energy electron diffraction (RHEED) intensity concluded that the surface roughening is a result of competition between surface roughening processes such as adsorption and evaporation and the surface smoothening process such as surface migration to stable sites. In this work, the stochastic model of MBE growth is employed to study the surface roughening kinetics in GaAs (100). The growth condition was chosen similar to that of experiments: temperature range of study: 773 – 873°K; cation to anion flux ratio in the range: 1 : 10 to 1 : 20. Diatomic arsenic molecular specie is employed for the study was As2. The time averaged RHEED intensity was obtained from the growth data and with the experimental results. The agreement between the results was excellent. A transition temperature at which the time averaged RHEED intensity is a maximum was observed for flux ratios 1 : 10 and 1 : 20. The RHEED intensity increases with temperature till the transition temperature due to surface smoothening resulting from the surface migration of Ga and As to energetically favorable sites. The RHEED intensity decreases beyond the transition temperature due to the evaporation of As from the surface. The transition temperature is observed to be a function of the flux ratio and can be explained by the difference in time for the formation of energetically stable surface adatom clusters resulting from the difference in the effective surface migration rates for various flux ratios.