In Electron Heating Modulation, a microwave field is applied to the active region of a semiconductor laser to change the electron temperature, and thereby to indirectly change the optical transition and to achieve high speed modulation. A detailed theoretical model by including the electron temperature has been developed to investigate this modulation scheme, and to identify the principal difference and limitations in comparison with the traditional scheme, Current Injection Modulation. Optical gain peaks for various electron temperature are calculated. Small signal analysis reveals that a semiconductor laser can be modulated beyond 50 GHz by electron heating, a few times higher than that by Current Injection Modulation. However, this benefit is not retained in large signal operation. In fact, in large signal simulation the modulation bandwidth by both schemes are shown to be similar, at 16 GHz. In view of the fact that the modulation bandwidth of conventional method is limited by the spontaneous recombination time, a method combining the Electron Heating Modulation and the Current Injection Modulation, is an intriguing alternative. Large signal simulations shows that there are some merit to this combined method.