To investigate and understand the reliability behavior of strained silicon devices, the changes of gate currents (Ig) and substrate currents (Isub) in n and p-channel metal-oxide-semiconductor field-transistors (MOSFETs) under different types of mechanically applied tensile stresses have been studied. It has been observed that, under the uniaxial tensile stress, both Ig and Isub of pMOSFETs increase with the increase of applied stress under the inversion and the accumulation conditions. However, an opposite stress dependence in nMOSFETs has been observed for Ig and Isub in both the inversion and the accumulation regimes. Similar changes have been found for Ig and Isub of nMOSFETs under biaxial tensile stress. The observations are explained by the strain induced band structure modulation and the repopulation of carriers.