The paper discusses the problem of rotor position estimation for the nonsalient permanent magnet synchronous motor (PMSM) and presents a Sliding Mode (SM) EMF observer that is based on the machine's model in the stationary reference frame. The speed of the PMSM which is an input of the proposed sliding mode observer is obtained from a speed estimator. The paper assumes that the speed estimate is different from the real speed and shows that the gains of the SM observer can be designed such that the EMF estimates produced by the SM observer tend to the real EMFs. The observer is designed and analyzed in the framework of nonlinear control using Lyapunov's theory and is validated using simulations. The method proposed is relatively simple and can be used to estimate the rotor position of the PMSM in a sensorless drive.