In this paper, we demonstrate for the first time ring laser oscillation using a set of silicon (111) mirrors fabricated by microelectromechanical systems (MEMS) technology with a semiconductor optical amplifier (SOA) as an optical amplifier medium. Four (111) mirrors were fabricated perpendicular to a (110) silicon wafer surface to form an optical loop. The (111) mirrors were fabricated by a combination of deep reactive-ion etching (DRIE) and anisotropic wet etching, followed by electroplating with a highly reflective Au film. Adjusting the mirror alignment for the oscillation was not required because the mirrors were already precisely positioned with the accuracy of the crystal orientation. In experiments, oscillation began at an injection current of more than 110 mA into the SOA. We confirmed that both forward and backward propagating lasers oscillated simultaneously in a single mode. Our results will especially be useful for realization of next-generation optical MEMS ring laser gyroscopes.