For high-power and high-frequency electronic applications, the III-V nitride layers are usually grown on sapphire or silicon carbide substrates. However, the development of these applications on silicon substrates has obvious technological advantages (cost, integration). In the present work, AlGaN/GaN heterostructures are grown on a resistive [111] silicon substrate (4000-10000 Ω.cm) in a reactive molecular beam epitaxy system using ammonia (Riber Compact 21). The structural quality of the epilayers as well as electrical properties have been investigated. AlGaN/GaN HEMT devices with different gate lengths and source to drain spacings have been realized in order to investigate their static characteristics and RF power performances.