Dielectric film quality is one of the most important factors that will greatly impact device performance and reliability. Device level electrical analysis techniques for dielectric quality monitoring are highly needed. In this paper we present results using a new electrical AFM mode, scanning Microwave Impedance Microscopy (sMIM), for characterization of device oxide quality and for fault isolation. Devices with poor oxide quality show sMIM nano C-V and dC/dV hysteresis behavior during forward and reverse bias sweep. The sMIM capacitance sensitivity is below 1 aF allowing one to capture C-V spectra from the MOS structure formed by the gate and gate oxide with excellent signal/noise ratio and observe subtle variations between different sites.