Permanent magnet synchronous motors (PMSM) are used in a great variety of applications such as: electric toys, electric tools, medical/chemical industries, centrifuges at high speed, vehicle applications (motor starters), robot applications etc. All these have in common small size, high energy density, increased torque for a large speed range, high dynamics when high inertia is present. In consequence, such machines are subject to high thermal stresses during their operation. If these stresses are known then it is possible to adjust the machine's control parameters (such as voltage and current) depending on the load and the supplying technique, in order to avoid overheating. The paper presents an analysis of the thermal regime of a PMSM when operated as an AC servo motor taking into consideration two different supplying techniques, a sinusoidal supply (which in the present study is considered to be the reference case) and a sin-PWM inverter supply. To facilitate a fully view of the motor's thermal behavior under the different supplying techniques, the analyses is performed for different speeds under the same load pattern.