Scanning nonlinear dielectric microscopy (SNDM) is a useful method for the nano-scale carrier distribution imaging of semiconductor materials and devices. This method is normally combined with contact mode atomic force microscopy (AFM) but the combination of SNDM with intermittent contact mode AFM is preferable to avoid the damages of tips and samples. However, signal-to-noise (S/N) ratio may significantly reduce due to a shorter contact time in the intermittent contact mode. Here we discuss the S/N ratio of the intermittent contact mode and show that the existence of the optimal condition on contact time and measurement bandwidth to maximize S/N ratio. We also experimentally demonstrate that signal intensity is actually improved by controlling contact time in the carrier distribution imaging on a Si test sample and atomically-thin layered semiconductors.