Based on the beam characteristics of semiconductor lasers, a new parameter for evaluating beam quality of high power semiconductor lasers was introduced. The shortcomings of M2 factor used in evaluating beam quality of semiconductor lasers were discussed and its limitations were pointed out. Moreover, some important aspects of the beam quality factor are discussed. The main factors which influence collimating the beam of semiconductor lasers are analyzed. The results suggested that the smaller the value of the new parameter is, the more easily the beam is collimated.