In this paper, we study the hole transport properties in strained-SiGe channel p-MOSFETs (sSG pMOSFETs) with a Si-cap layer, which is introduced to avoid degradation of interface quality between gate oxide and channel. By using device simulation considering Ge diffusion, quantum confinement effects, surface roughness scattering and Coulomb scattering due to interface charges, and also experimental measurement, we clarify the roles of a Si-cap layer in sSG pMOSFETs, and furthermore propose its optimized design to obtain a higher device performance. We also demonstrate that the insertion of a Si-cap layer is effective to reduce an OFF-state leakage current owing to an increased band gap energy in the Si-cap layer. (C) 2013 Elsevier Ltd. All rights reserved.