This paper explains the importance of device size and dc bias conditions for the gain and linearity performance enhancement of silicon based RF amplifiers. In this work, the existence of an optimum device size for maximum gain, for the given bias conditions and load impedances is explained by determining the small-signal gain parameters for a common source amplifier as functions of the device size and dc bias conditions. Also, the change of optimum device size with the bias conditions and the load impedances is analyzed. A Taylor series expansion is used to determine the extent of weak nonlinearity for different device sizes. IP3 measurements suggest that the distortion is minimum for a particular device size. The analysis presented in this paper enables the optimization of the performance of Si-MOSFET based RF amplifiers.The frequency chosen for analysis is 2.4GHz.Index Terms—Gain, linearity, RF amplifiers, small signal, device size.