Device operations of the monolayer molybdenum disulfide (MoS2) based FETs are analyzed using first principle atomistic simulations, revealing the similarity of device operation in monolayer and Si transistors. Taylor expansion is employed on Si potential modeling framework, assuming an ultra-thin (delta function like) channel for MoS2 devices. The method accurately reproduces the gate control of the MoS2 FETs in both long channel and short channel transistors including the subthreshold characteristics. First principle simulations verify the developed model, suggesting that the monolayer MoS2 MOSFET can be modeled by extending Si MOSFET equations with incorporating material parameters.