This study theoretically examines the hole subband structures in inversion layers of strained Silicon (Si) transistors under different strain conditions. Two strain conditions of Si P-channel metal-oxide-semiconductor (PMOS), including intrinsic strain resulting from growing the Si on the (001) Silicon-Germanium (SiGe) substrate and mechanical stress applied externally, were considered in this work. Various effective masses of hole inversion layers used in technology computer-aided design (TCAD) simulations were investigated, such as the quantization effective mass, m(z), the density of states effective mass, m(DOS), and the conductivity mass, m(sigma). It was then demonstrated that the external stress applied parallel to the channel direction for holes in the inversion layer with intrinsic biaxial strain is an optimal method of lowering m(sigma) and increasing m(DOS) for the top subband. (C) 2009 Elsevier B.V. All rights reserved.