Recent strong demands for optoelectronic communication and portable telephones have encouraged engineers to develop optoelectronic devices, microwave devices, and high-speed devices using heterostructural compound semiconductors. Although the compound crystal growth techniques had reached at a level to control the compositional stoichiometry and crystal defects on a nearly atomic scale by the advanced techniques such as molecular beam epitaxy and metal organic chemical vapor deposition techniques, development of ohmic contact materials (which play a key role to inject external electric current from the metals to the semiconductors) was still on a trial-and-error basis. Our research efforts have been focused to develop, low resistance, refractory ohmic contact materials using the deposition and annealing techniques for n-GaAs, p-ZnSe, InP, p-SiC p-CdTe etc. It was found the growth of homo- or hetero–epitaxial intermediate semiconductor layers (ISL) was essential for low resistance contact formation. The importance of hetero-structural ISL was given taking an example of n-type ohmic contact for GaAs.