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In this paper, we calculate the surrounding strain effects owing to gate dielectric on the device performance of Si nanowires (NWs) with different axial orientations. Surrounding strain effects from valence band structure to hole transport property of NW FETs are developed. The simulated results show that surrounding strain pushes the valence subbands upward. The upshifting trend of the valence subband maximum is (1 1 0) NW >; (0 0 1) NW >; (1 1 1) NW. The shift coincides with the εzz variation, which contributes the most to modulate the valence subbands. Compared to pure Si NWs, surrounding strain owing to HfO2 dielectric enhances the effective hole mobility. Effective hole mobility enhancement in HfO2 surrounding Si NW is (0 0 1) NW >; (1 1 1) NW >; (1 1 0) NW. However, Si(1 1 0) NW still has the largest effective hole mobility among three axial orientations.