We present two methods for mapping strains in MOSFETs at the nanometer scale. Aberration-corrected high-resolution transmission electron microscopy (HRTEM) coupled with geometric phase analysis (GPA) provides sufficient signal-to-noise to accurately determine strain fields across the active regions of devices. Finite element method (FEM) simulations are used to confirm our measurements. The field of view is however limited to about 100 nm2. To overcome this, we have developed a new technique called dark-field holography based on off-axis electron holography and dark-field imaging. This new technique provides us a better strain resolution than HRTEM, a spatial resolution of 4 nm and a field of view of 1 μm.