The laser device (22) is formed by a stack of laser diodes (4) arranged on plates (6) formed of a material that is electrically conductive and a good heat conductor. In order to obtain a high level of heat evacuation efficiency towards the cooling body (10) and to prevent electric short-circuiting problems, each plate has at the bottom end (24) thereof, an electrically insulating layer deposited on the surface thereof prior to being fixed to the cooling body by a securing material (26) that is preferably a good heat conductor, formed in particular by a braze layer. According to the invention, the insulating layer covers the end face of each plate and also goes up along the lateral faces of the latter over a certain height. The securing material is arranged under the end of the plate and also partially covers the insulating layer along the lateral faces of the plate.