Abstract : This work talks about the shape memory alloys (SMA) used as actuators in microrobots and microsystems. Among the SMA the nickel-titanium alloy (NiTi) is a very good material useful in particular for actuation. It is able to provide a very important mechanical work in comparison with the other active materials. However, considering that the temperature is its control parameter the response time of the SMA is great. Moreover, it is very difficult to control precisely its displacement because the SMA is very sensitive to the thermal external conditions. Therefore, this work contains a thermal study, using the physical model of a SMA, of the two main principle that are efficient for heating and cooling this material : the Joule effect and the Peltier effect. This study has leads to the realization of a micro-actuator that have an integrated Peltier System (named Peltier $\Omega$ module). This original actuator has the particularity to be less sensible to the external temperature variations and can work in confined environments witch is impossible with a Joule actuator. A numeric simulator that has been developed in this study, help to understand and to predict the thermomecanical behavior of the $\Omega$ module.