The ability to measure subtle changes in arterial pressure using devices mounted on the skin can be valuable for monitoring vital signs in emergency care, detecting the early onset of cardiovascular disease, and continuously assessing health/wellness. Conventional technologies are well-suited for use in traditional clinical and laboratory settings, but cannot be easily adapted for application during daily activities. In this paper, we introduce materials and designs for a conformal device that avoids this limitation. We present inorganic materials, heterogeneous designs and theoretical models for an ultrathin, compact device capable of softly laminating on the skin. These systems are small (~1 cm2), lightweight (2 mg), thin (25 µm), and capable of stretching (to ~30%, with system-level effective modulus of ~60 kPa) to conform to the skin, while providing high levels of pressure sensitivity (~0.005 Pa), fast response times (~0.1 ms), low hysteresis, superior operational stability, and excellent fatigue properties. Ultrathin (400 nm) sheets of high-quality PZT serve as the active components of capacitor type structures that connect to the gate electrodes of MOSFETs based on nanomembranes of silicon (SiNMs). Specifically, a SiNM n-channel MOSFET amplifies the piezoelectric voltage response of the PZT and converts it to a current output via capacitance coupling. Comprehensive electromechanical measurements and theoretical models provide complete descriptions of the principles of operation, including enhanced piezoelectric responses in PZT when mounted on soft substrates. Calibrated measurements of pressure variations associated with blood flow in near surface arteries demonstrate capabilities for measuring blood pressure, radial artery augmentation index and pulse pressure velocity. Quantitative correlations of data from the former class of measurement to those of conventional devices suggest opportunities in continuous, non-invasive monitoring of pressure transients associated with arterial blood flow.