This article successfully demonstrates the efficacy of using recently developed MEMS phase shifters for submm-wave phased arrays. An improved MEMS phase shifter design is presented with a measured 350∘ phase shift in the 500-600 GHz band. As a demonstrator for dynamic beam-steering with MEMS phase shifters, this article presents the design, fabrication and characterization of a linear, near-Nyquist sampled 4x1-element phased array using leaky-wave feeds for enhanced directivity and reduced grating lobes. It is shown that the feed is also suitable to use in larger 8x1 arrays to achieve 20 dB gain and ±20 deg scanning with a fan beam for applications such as THz communications. The MEMS phase shifters are ideal candidates for integration with high gain scanning-lens phased arrays for future space-borne spectroscopy instruments.