Sensorless induction motor (IM) drives are widely used in industry for their reliability and flexibility, particularly in hostile environment. However, the performance of many of previously developed observer based speed sensors in very low speeds of IM drives was not satisfactory. In this paper, the model reference adaptive system (MRAS)-based speed and stator resistance estimators of IM drives fed by four switch three phase inverter (FSTPI) in the critical low and zero speed region of operation are presented. The estimated speed is used as feedback in a vector control system. The MRAS approach has the immediate advantage that the model is simple, eliminates the produced error in the speed adaptation, and more stable and robust. Simulation results of the MRAS speed observer based sensorless field-oriented induction motor drives fed by FSTPI are presented at critical low and zero speed region of operations. The performances of the MRAS technique is evaluated in indirect vector control system. Experimental results validate the proposed approach.