Provided is a method of fabricating a laser diode including a lower Al-containing semiconductor material layer, a active layer, and an upper Al-containing semiconductor material layer. The method includes thermally cleaning the inside of a deposition reactor in which a substrate on which the lower Al-containing semiconductor material layer is stacked is loaded. During the thermal cleaning process, the inside of the deposition reactor is thermally treated at a predetermined temperature in an atmosphere of a gas mixture of AsH.sub.3 and H.sub.2 that is injected into the deposition reactor.