This paper presents a study of the stable gain selection of a position sensorless control based on back-electromotive force (back-EMF) estimation in an interior permanent magnet synchronous motor (IPMSM). The characteristic of the estimated back-EMF signals is analyzed using various mathematical models of the IPMSM. The sensorless control based on the extended EMF model in the rotor reference frame has back-EMF estimator such as a disturbance observer, and rotor position estimator such as a phase-lock-loop (PLL) type estimator. To ensure the stability of sensorless control, the selection methods of major factors for sensorless control algorithm are introduced. The feasibility of the proposed strategy is verified through simulation and experimental results.