An object is to provide a semiconductor device and its manufacturing method in which delay in switching and non-uniform operations are prevented and in which stresses occurring in trench regions are alleviated as much as possible. A gate electrode in a gate trench is formed of a polysilicon layer and a gate tungsten layer that is lower resistant than the polysilicon layer. Also, a source electrode is formed of source tungsten layers buried in source trenches and an AlSi layer in contact with the source tungsten layers and covering source layers and the gate electrodes with a thick insulating film interposed therebetween.