A method of forming a low temperature-grown buffer layer having the steps of: placing a Ga.sub.2O.sub.3 substrate in a MOCVD apparatus; providing a H.sub.2 atmosphere in the MOCVD apparatus and setting a buffer layer growth condition having an atmosphere temperature of 350.degree. C. to 550.degree. C.; and supplying a source gas having two or more of TMG, TMA and NH.sub.3 onto the Ga.sub.2O.sub.3 substrate in the buffer layer growth condition to form the low temperature-grown buffer layer on the Ga.sub.2O.sub.3 substrate.