The III-V compound semiconductor is always relatively popular material due to its many interesting optical and electrical properties. On the other hand, there has been a longest evolution history of Si in the current semiconductor industries, a defect-free silicon material can be achieved technologically. The silicon material has many merits that can not be found in III-Vs, such as good heat dissipation capability, strong and not easy to crack, and the material can be purchased easily, etc. Otherwise, if the substrate used now can be replaced by the silicon, then the cost of substrate material will be largely reduced. In other words, these advantages of Si substrates can open up applications of III-Vs, such as OEIC, solar cells, and light emission/detection devices, etc. Therefore, in this book, the heteroepitaxial growth of III-V compound semiconductors on Si substrate by atmospheric-pressure metal-organic chemical vapor deposition (AP-MOCVD) is reported. The investigations arefocused on the growth of three typical monocrystalline materials including GaAs, GaN and InN. Besides, the fabrication of two polycrystalline films of GaN and TiN will also be described.