This paper deals with the Permanent Magnet Synchronous Motor (PMSM) observability analysis for sensorless control design. The problem of loss of observability at low frequency range is always recognized in experimental settings. Nevertheless, there are no sufficient theoretical observability analyses for the PMSM. In the literature, only the sufficient observability condition has been presented. Therefore, the current work is aimed especially to the necessary observability condition analysis. Furthermore, improved zero-speed observation is presented here for a Surface PMSM (SPMSM) to overcome position observability problems at zero-speed which is an unobservable state point. The proposed observer based on Higher Order Sliding Mode (HOSM) is designed in order to ensure the robustness against disturbances and to avoid the chattering phenomenon which is inherent in standard first order sliding mode. The stability and finite time convergence of the developed observer are studied and discussed. Experimental results are carried out to illustrate the effectiveness and robustness of the proposed observer.