A new aluminum nitride (AIN) substrate, which has high thermal conductivity of 160 W/mK at room temperture, has been developed using the hot press sintering technique. The new AIN substrate has the following excellent characteristics. 1) The thermal conductivity is eight times as high as that of AI 2 O 3 at room temperature and is almost equal to that of 99.5 percent BeO at 150°C. 2) The thermal expansion coefficient is smaller than that of AI 2 O 3 and BeO, and is close to that of a silicon semiconductor chip. 3) The electrical properties are almost as good as those for AI 2 O 3 and BeO in the wide frequency range. 4) It not only has higher mechanical stength but also easier machinable property than AI 2 O 3 . It is characterized by its light transparency from visible light to the infrared wavelength region. It was proved that the new AIN substrate is able to be metallized with good adhesion strength by the conventional evaporating method and the conventional sputtering method. The new AIN was found to be applicable to three kinds of semiconductor devices: 1) silicon epitaxial transistor, 2) GaAIAs light emitting diode, and 3) InGaAsP laser diode. Also, another AIN substrate was developed using the normal sintering technique, which has high thermal conductivity of 140 W/mK at room temperature.

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